Pyriproxyfen (PPF) is a juvenile hormone analogue insecticide that is often used as a larvicide against a wide range of insect pests. The present study was designed to investigate its teratogenic effects on the embryonic development of the chick. First, the median lethal dose (LD₅₀) of the commercial PPF was determined. Accordingly, three sub-lethal doses (15, 30, 45 µg/egg) were selected for injection into the air space of the eggs after 24 hours of incubation. The eggs were opened on the embryonic days (EDs) 7 and 14, and the embryos were examined for morphometric changes and the presence of malformations. The PPF treatment induced growth retardation and reduction in head and eye sizes as reflected by a reduction in wet body weights, crown-rump lengths, anterior-posterior head lengths, and eye diameters. These morphometric alternations were mild or moderate on ED7, but more apparent on ED14. Also, significant reductions in the lengths of the forelimb and hindlimb parts were recorded with high-dose treatment on ED14. Obviously, there was high percentage of malformations among ED7 individuals in the form of hematoma, ventral body wall defect, limb deformities, microphthalmia, and microcephaly. However, on ED14 the embryos exhibited significant hematoma, microcephaly, delay feather, delay beak, microphthalmia in all treated groups, and limb deformities in the group that received the high dose. Other abnormalities included edema, anophthalmia, short neck, short tail, caudal regression, microtia, and microblepharon were also recorded. These findings revealed that PPF has potentially teratogenic effects on the development of the chick embryos.