OBJECTIVE To study the effects of prenatal exposure to benzo[a]pyrene (B[a]P) on the physical development, early behavioral development, the adaptability to new environment and the learning and memory ability of rat offspring. METHODS Pregnant rats were randomly divided into five groups: control group, olive oil group, 3 exposure groups (25, 50 and 100 mg/kg B [a]P). The rats were exposed to B [a]P) by intraperitoneal injection on the 17th-19th days during gestation. The offspring were weighed on postnatal days (PND)1, PND 4, PND 7 and PND 28, the indices of physical development, reflective ability and sensory function were detected for offspring, the Morris water maze and Open-field tests were used to measure the ability of learning and memory and the adaptability to new environment of offspring. RESULTS The time of ear opening in middle and high-dose groups [(4.1 +/- 0.4),(5.0 +/-0.4) d] was posterior to that in untreated and solvent groups [(3.3 +/- 0.5), (3.4 +/- 0.6) d ](P < 0.01). The attainment rate (6.5%) of the surface righting reflex test in high-dose group on the 4th day was significantly lower than that (36.1%) in untreated group, the attainment rate (50.0%) in high-dose group on PND7 was significantly lower than those (81.3% and 79.3%) in untreated group and solvent group (P < 0.05). Compared to the untreated group, the time of forelimb hanging test in all exposure groups on PND12 and PND14 significantly decreased; compared to the solvent group the time of forelimb hanging test decreased in high-dose group on the 14th day significantly decreased (P < 0.01). The attainment rate (61.9%) of olfactory discrimination in high-dose group on PND12 was significantly lower than that (94.3%) in untreated group (P < 0.05). The results of Morris water maze test showed that the escape latency of different dose groups significantly increased, and the time of spatial probe and the times of traversing flat in high-dose group decreased significantly, as compared to the untreated and solvent groups (P < 0.01). The results of open-field test indicated that the center retention time in middle and high-dose groups significantly prolonged, the times of crossing lattice obviously reduced, and the rearing times decreased in high-dose group, as compared to untreated (P < 0.05).Compared to the solvent group, the times of crossing lattice in all exposure groups reduced significantly (P < 0.01 or P < 0.05). CONCLUSIONS The prenatal exposure to B[a]P could inhibit the physical development and early behavioral development, and influence the adaptability to new environment and learning and memory ability for offspring.