Abstract: Pyronaridine was administered to rats orally in doses of 84, 165 or 330 mg/kg/d for 3 consecutive days or in a single dose of 1100 mg/kg beginning from D₇ of gestation. A known teratogen, N, N'-methylene-bis-(2-amino- 1, 3, 4- thiadiazole), dexon, at a dose of 5 mg/kg/d×7 was used as positive control. Pregnant rats were sacrificed on D₂₀ and fetuses subjected to teratological investigation. The results showed that pyronaridine at all the dosages could increase dose-dependently the rate of fetal resorption. It could also delay the ossification of occipital bone and sternum of the fetuses. Neither altered appearance nor dysmorphosis of viscera and skeleton were noted in all the test groups. It is presumed that pyronaridine possesses potent embryotoxicity under the present experimental conditions.