In order to estimate the genetic parameters for different agro-morphological traits in flax, a complete diallel cross was conducted by using eight flax genotypes including four Iranian breeding lines and four Canadian genotypes. Analysis of variances showed highly significant differences among the genotypes. Significant general combining ability (GCA), specific combining ability (SCA) and reciprocal effects revealed meaningful contributions of both additive, non-additive type of gene actions and also the maternal influence in genetic control of the traits. The results showed that additive gene actions had greater effects on the inheritance of days to flowering, days to maturity, plant height, primary branches per plant, 1000-seed weight, seed oil content, linoleic acid and stearic acid in the oil. However, number of capsules per plant, number of seeds per capsule, palmetic acid and oleic acid content in the oil and LDP ODP indexes were largely controlled by dominance genetic effects. Both additive and non-additive gene actions were important in genetic control of harvest index, seed yield per plant, seed and oil yield. Base on the values of GCA, the best parental combiners were McGregor for plant height, KO37 for 1000 seed weight, early flowering and maturity, KH124 and KO37 for number of seeds per capsule, seed oil content, seed yield per plant and seed yield, AH92 for branches per plant and ODP indexes, SE65 for number of capsules per plant. A considerable heterosis was observed for the studied traits in some cross combinations and the highest heterobeltiosis values of 64.1, 35.1, 21.6, 77.2 and 91.3% were obtained for number of capsules per plant, number of seeds per capsule, 1000-seed weight, seed yield per plant and seed yield, respectively. The results of generation mean analysis for two crosses also indicated that plant height, branch per plant and 100 seed weight, number of seeds per capsules and seed yield per plant were controlled by both additive and dominance genetic effects, whereas, non-allelic gene actions showed considerable effects on number of capsules per plant. These results imply the potential of producing superior cultivars through selection in segregating populations or using the hybrid cultivar advantages, providing that the technical problems hampering economical production of hybrid seeds in flax could be overcame