The purpose is to evaluate the effects of di-2-ethylhexyl phthalate (DEHP) on the spatial learning and memory of offspring rats and on expressions of hippocampal synaptic plasticity related genes in rat's hippocampi by lactation exposure and explore the molecular mechanism of this process.Methods Mated female rats were assigned to four groups of 8 animals each based on a weight-balanced random allocation scheme after copulation. Mated female rats were administered different concentrations of DEHP (0,5, 50,0 mg/kg BW) by oral gavage with a metal catheter from PND 1 through PND 21. Spatial learning and memory were measured continuous 6 days for young adults (PND 65 days to 70 days) with Morris water maze and the effects on expressions of hippocampal synaptic plasticity related genes mRNA in rats′ hippocampi were detected by Real-Time PCR. Results In the location-navigation test in Morris maze,the latency time of 500 mg/kg BW group was longer than control group, and there was statically significant difference (P<0.05). In the spatial probe test, the distance percent in the target quadrant, time percent spent in the target quadrant and the frequency of crossing platform of 500 mg/kg DEHP group were less compared with control group (P<0.05). According to the data of Real-Time PCR, comparing with control group, the expressions of hippocampal synaptic plasticity related PSD95, CREB, PKA and CAMKII mRNA in 50 and 500 mg/kg BW groups were significantly down-regulated respectively (P<0.05). The expression of hippocampal synaptic plasticity related BDNF was down-regulated in 500 mg/kg DEHP group compared with control group (P<0.05).Conclusion Lactation exposure to DEHP (500 mg/kg BW) could produce developmental neurotoxicity and has effect on spatial learning and memory of offspring rats. The inhibition of expressions of hippocampal synaptic plasticity related genes such as PSD95, CREB, PKA, CAMKII and BDNF could be the mechanism of this process.