Melon (cantaloupe), Cucumis melo L. is one of the most economically important species of Cucurbitaceae, which is mostly cultivated in arid and semi-arid regions of the world, where the challenging abiotic stresses such as salinity are present. To our knowledge, there has not been yet any reported comprehensive study on salinity tolerance of indigenous cultivars and genetics of salinity tolerance in melon under field conditions. The present study was conducted to evaluate genetic and physiology of the economically important and salinity tolerance related traits. In the first experiment, 16 native melon cultivars collected from different regions of Iran and one exogenous cultivar (‘Galia’) were evaluated in terms of agronomic and physiological characteristics under the open normal and saline field conditions at the Lavark Research Station, College of Agriculture, Isfahan University of Technology, Isfahan, Iran during two-growing seasons. Salinity treatment was applied through irrigation with saline water (EC w =14 dSm -1 ). The results revealed high genotypic variation for the evaluated traits, including morphological, agronomic, phenological, quality and salinity tolerance related traits. Most of the studied traits were significantly affected by salinity stress. The results of principal component analysis showed the factors that contribute to higher yield under salinity include lower yield loss, low concentration of Na + , high concentration of K + and high K + /Na + ratio. ‘Sabouni’ and ‘Shahabadi-1’ cultivars were found to be the most salinity-tolerant cultivars. These tolerant cultivars also had the highest relative water content (RWC), membrane stability index (MSI), salinity tolerance index (STI), and the lowest malondialdehyde content (MDA), hydrogen peroxide (H 2 O 2 ) and salinity susceptibility index (SSI) under stress conditions. Therefore, they can be used as suitable cultivars for production under saline conditions or as parents in salinity tolerance breeding programs. The results of multiple regression analysis showed that the main components of yield (fruit weight and fruit number), MDA content and leaf Na + concentration were the most important factors in salinity tolerance. The second experiment was carried out with intercrossing 11 selective melon cultivars with different levels of tolerance using a 11 × 11 half diallel design. The resultant hybrids along with parents (55 hybrids and 11 parents) were planted in a simple rectangular lattice design for each normal and saline field conditions and various agronomic and physiological traits were evaluated. High genetic variation was observed for all of the studied traits. The results of diallel analysis based on Griffing and Jinks-Hayman methods showed that both additive and non-additive gene effects are involved in the controlling the traits. According to the genetic ratio, additive and dominance variances, and also heritability estimates, non-additive effects were more important in governing the traits except fruit weight, fruit width, seed cavity width, flesh thickness and total soluble solids in normal conditions. In saline condition, all the traits with the exception of fruit crown length, days to maturity, fruit width, seed cavity width and flesh thickness were controlled by a much higher non-additive gene action. ‘Rishbab’, ‘Sabouni’, ‘Till-Toroq’ and ‘Dastjerdi’ parents in normal conditions and ‘Shahabadi’, ‘Dastjerdi’, ‘Sabouni’, ‘Savehie’ and ‘Rishbaba’ parents in saline conditions were the superior general combiners for the major economic traits, fruit quality and salinity tolerance related physiological traits. These parents can be employed to improve the traits by accumulating alleles with additive gene effects in a recurrent selection program. The hybrids Shahabadi × Dastjerdi, Magasi × Majidi-Abarkouh, Till-Toroq × Savehie and Savehie × Sabouni in normal conditions and Shahabadi × Dastjerdi, Magasi × Dastjerdi, Magasi × Majidi-Abarkouh and Till-Toroq × Savehie in saline conditions showed the highest specific combining ability (SCA) and heterosis for most of the traits. In the third experiment, fruit sugar components of selected parents and their hybrids grown in normal and saline conditions were assessed using high performance liquid chromatography (HPLC) method. The results showed that salinity stress caused a significant increase in sucrose, glucose and fructose concentrations leading to higher fruit sweetness viz fruit sugar and total soluble solids. In addition, the high heritability estimates for total soluble solids and sugar components revealed the high impact of additive gene effects in controlling these traits. Key words: Melon, Sugar components, Physiological traits, Diallel analysis, Gene action, Heritability.