N-methyl-N′-nitro-N-nitrosoguanidine(MNNG) and Ethidium Bromide(EtBr) were fed to Drosophila melanogaster in order to investigate their toxic capacity at developmental and adult stage, and potency for the induction of X-linked lethal mutation during the spermatogenesis. Both MNNG and EtBr were highly toxic at developmental and adult stage resulting in prolongation of the developmental time and lowering of the viability, and high mortality of adults as the dose increased. The toxic capacity of MNNG was fairly higher than EtBr in developmental stage but an reverse aspect in adult stage. In the induction of X-linked lethal mutation during the spermatogenesis, MNNG had more pronounced effect in the sperm and spermatid, and EtBr did in the spermatid and spermatocyte stage, respectively.