Three field experiments were carried out at the Experimental and Research Station, Faculty of Agriculture, Cairo University in Giza during 2001, 2002 and 2003 seasons to study the effect of some mutagens on morphological and yield traits of sesame and to estimate the genotypic and phenotypic coefficients of variation, broad sense heritability and genetic advance from selection for several important traits in sesame mutant populations (M₂ and M₃ generations). Two commercial cultivars viz., Giza 32 and Toshka 1 were treated with (gamma rays) and ethyl methane sulphonate (EMS) mutagens. The results revealed significant differences among the mutagenic treatments across mutated generations with regard to their effect on plant characteristics under study. The results indicated that sesame cultivars may be treated safely at 400 Gy and 500 Gy (gamma rays) and at 0.5 and 1.0% (EMS), and for obtaining positive mutations. Selection of mutants in the segregating M₂ generation exhibited a number of useful sesame mutants. These mutants include: mutants with plant habit (determinate), short flowering period-type (early maturing) and mutants with more capsules per plant, long capsule, multi capsules per leaf axil, multi carpellate, shortened internodes and semi shattering capsule. Coefficient of variability indicated that seed yield per plant, number of capsules per plant, number of fruiting branches, flowering date and fruiting zone length were greatly affected by mutagens than oil content and 1000-seed weight. Estimates of phenotypic coefficient of variability (PCV) was generally higher than the genotypic coefficient of variability (GCV) for all studied traits but the difference was small, indicating little influence of environment in the expression of these characters. The PCV and GCV estimates were the highest for number of capsules per plant and seed yield per plant. Low values in this respect were recorded for days to flowering, 1000-seed weight and seed oil content. Estimates of correlation coefficients revealed that highly significant and positive correlations were found between seed yield per plant and each of number of capsules per plant, fruiting zone length, number of fruiting branches and plant height, suggesting that seed yield per plant is a function of these parameters and selection based on these traits could further improve the yield potential. High heritability and genetic advance estimates were observed for plant height, number of branches per plant, number of capsules per plant and seed yield per plant in M₂ and M₃  generations, indicating the effectiveness of selection for the improvement of these traits.