Medicinal plants are considered as a genetic reservoir in Iran. Among these, mint scientifically named Mentha of the Lamiaceae family, is a perennial and one of the most economically and medicinally important plants that is widely distributed throughout the world, especially in the Mediterranean region. Mint is naturally outcrossing; however, production of selfed seeds may have many economic and breeding benefits. The aim of this study was to investigate selfed-seed production in previously selfed offspring of mint genotypes and seedling production of selfed seeds, as well as evaluation of populations resulting from mint selfing and genetic variation and degree of inbreeding depression effect on morphological traits in two successive generations. In this regard, 4 clonal populations of mint were utilized that were originally collected from Ahvaz, Lorestan, Karaj and Hamadan in the previous research. The populations of this study consisted of two genotypes of Mentha spicata and two genotypes of Mentha longifolia that were self-pollinated for two generations and were evaluated along with their parental clones. This research was conducted in two parts, during the years 2018-2019. In the first part, the S 1 populations were evaluated in a randomized complete block design with three replications in the field located at the Lavark Research station of Isfahan University of Technology. In this evaluation, the best self-pollinating plants (S 1 ) were selected for re-selfing (S 2 ) using principal component analysis based on seed traits. The second and main part was to investigate the rate of depression induced on morphological traits, included S 1 , S 2 and parental populations (controls) that was performed cording to a preliminary Augmented design (incomplete block design). Results of ANOVA showed that the effect of adjusted genotypes was significant for most of the traits including height, spike length, leaf width, spike number, leaf area, fresh weight, dry weight, height to branch number ratio and fresh weight to dry weight ratio, indicating high variation among the genotypes. In the study of the rate of depression, in Ahvaz genotype of M. spicata , most of the traits, especially fresh and dry weight, leaf area, height, spike number and lateral branches in S 1 and S 2 populations had higher values compared to their parents indicating genetic improvement in these traits due to selfing. In Lorestan genotype of M. spicata , fresh and dry weight, leaf area and canopy diameter in S 1 and S 2 populations were significantly higher than those in their parents showing the genetic improvement in Lorestan genotype in both generations. There was a considerable variation in S 2 population regarding these traits. In Karaj genotype of M. longifolia , only in fresh and dry weight, there was a significant variation compared to their parents. In the Hamadan genotype of M. longifolia species, self-pollination made some improving variation in the populations obtained, especially in S 2 , although some traits were also depressed. In analysis of the principle components of Ahvaz genotype of M. spicata , it was led to the selection of the best lines derived from self-pollination including lines #3, #4 and #5 which were those with high fresh and dry weights and high leaf area and with suitablity for medicinal and vegetable uses. They could be suggested instead of Ahwaz clonal genotype for cultivation. In Lorestan genotype of M. spicata , lines #3 and #4 were selected as superior lines, again having more fresh and dry weight and especially high leaf area compared to the preliminary parent. In Karaj genotype of M. longifolia , lines #6 and #7 and in Hamadan, line #2 were selected as the superior lines for the most traits. The results of cluster analysis in all S 1 and parental populations indicated that in some traits, M. spicata and M. longifolia are similar, possibly due to their similar genetic background. This study showed that it is possible to exploit from the high variation made by selfing in mint genotype to select the superior genotype for furthure breeding programs. Keywords: Mentha , self-pollinating, inbreeding depression, Genetic diversity, Genetic improvement