A comparative study was made to determine the spectrum and frequency of different mutants induced by gamma rays in three genetic backgrounds of sesame and to test the hypothesis that “closed capsule mutants are inducible with efficient mutagenesis and screening large populations”. Treatments concerned seeds of the two cultivars “32-15” and “38-1-7” extensively grown in Senegal and a recently released Turkish cultivar, “Birkan”, irradiated by two doses (300 and 400 Gy) of gamma rays. Both irradiated and untreated seeds (control) were sown greenhouse to raise the M1 populations. The M2 populations produced from the bulked M1 plants at harvest were grown twice under irrigated conditions in two sets; first set in Antalya, Turkey, in 2008 and the second set in Bambey, Senegal, in 2009. The selected potential mutants in the 2-set of M2 populations were grown in the M3 stage in Bambey to confirm their true breeding behaviour. Results indicate that the mutants confirmed shared a wide and unique spectrum of the mutants such as closed capsules, branching habit, flowering types, capsule number and shape. Also at least one closed capsule mutant could be induced from each of the three genetic backgrounds of sesame tested. Among the cultivars tested “38-1-7” had the highest total mutant frequency (5.6 x 10-3 ) followed by “Birkan” (4.2 x 10-3 ). The lowest mutant frequency (2.7 x 10-3 ) was recorded in “32-15”. From these results, it appears that medium dose range of gamma rays was enough to induce viable and useful mutations in sesame.