The performance of sterile males is one of the important topics for the successful use of the sterile insect technique. Silymarin (Sm) as antioxidant could play an effective role in ameliorating the physiological damage of B. zonata cells that may be induced during raring the colony and/or irradiation treatment. Different Sm concentrations (0, 10, 30, 50, 80 and 100 mg/kg) were added to the larval diet to study its impact on the reproductive biology and fitness of B zonata. Also, the radio-protective activity of Sm was firstly tested through studying the quality control parameters of the adult flies irradiated with the sterilizing dose levels (0,70, 90, 100 and 110 Gy) that previously fed on Sm in larval stage. Secondary, the protective effect of Sm were evaluated through ultrastructure studies of the male testes. The results indicated that additives of 80 and 100 mg/kg Sm concentrations increased the pupal and adult recovery, they were significantly increased to (77.2 and 76.2%) and (69.7 and 68.2%), respectively as compared to (72.2%) and (63.3%) in the control treatment, respectively. The results also revealed that in 80 mg/kg Sm concentration, the percentages of hatched eggs were increased either alone or in combined with the different sterilizing doses. Moreover, the adult flight ability and emergence percentages were increased in the all combination treatments. The ultrastructure study showed an improvement of the testis irradiated with 90 Gy when combined with 80 mg/kg as compared to the radiation treatment alone.