Abstract: Groups of 10 male mice were administered orally with pyronaridine phosphate at 3 dose regimes; 343 mg (base)/kg/d (1/4LD50 in mice, 30 times the clinical daily dose)x 3, 171.5 mg/kg/d x 3 and 86 mg/kg/d x 3. After the withdrawal of pyronaridine, each male mouse was caged together with 2 female mice for 1 week, then mated with another 2 females for 1 week until 5 matings were conducted. All the female mice were sacrificed and examined on the 15th day from the beginning of mating for viable fetuses, dead fetuses, implantations and early resolved embryoes. Of the 10 male mice treated with 343 mg/kg/d x 3 pyronaridine, one died of marked intoxication. In comparison with the control, the percentage of females with implantation (gestation rate), average implants, average live fetuses and fetus death rate showed no apparent effect of pyronaridine on male's gametogenesis or fertilization.