Objective: To investigate the effect of cerebral X-ray irradiation on learning and memory function in young rats. Methods: Fifty-four SD rats aged 35 d were randomly divided into 3 groups with 18 in each group: rats in 3-d group and 7-d group received X-ray irradiation with a dose of 28.5 mGy/d for 3 d and 7 d, respectively; rats in control group received sham X-ray irradiation. Morris water maze （MWM）was tested when animals at age of 60 d; then the animals were sacrificed and brain samples were taken. The neurodegeneration was observed by Fluro-Jade B staining; the expression of N-methyl-aspartate （NMDA）receptors subunit 2B （NR2B）and postsynaptic density protein-95 （PSD-95）in the hippocampus were analyzed by immunofluorescence and Western blot methods, respectively, and ultrastructure of CA1 region was observed with electron microscopy. Results: No significant difference in 1-4 d escape latency as shown in MWM test was noted between 3-d group and control group （P＞0.05）; while the escape latency in 7-d group was significantly longer than that in control group （P <0.01）. No significant differences in lingering in the quadrant and the frequency of passing through the original platform between 3-d group and control group （P＞0.05）, while those in 7-d group were significantly lower than those in control group （P＜0.01）. Compared to control group, the number of FJB positive cells in 7-d group was increased （P＜0.01）; the expressions of NR2B and PSD-95 in hippocampus CA1 region were also increased （P＜0.05）. The ultrastructure observation in 7-d group showed that the synapse structure of some neurons was impaired. Conclusion: X-ray irradiation may affect learning and memory function of young rats, which is associated with overexpression of NR2B and PSD-95 in hippocampal regions.