Objective To explore the dynamic change and correlation of the behavior and hippocampal volumes by MRI of rat depressive model. Methods Based on the evaluation of ethology, thirty SD rats were randomly and equally divided into control group and model group which was exposed to chronic unpredictable mild stress for 8 weeks. The body weight, fluid consumption test and Morris water maze test were done at the beginning and per week while the bilateral hippocampal volumes of every rat were measured by high field MRI at the beginning and per two weeks. Results Based on the behavioral data,the rat depressive model was established successfully,and changed dynamically. On 4th week,the left hippocampal volumes of depressive rat were significantly reduced (model group(37.13 ±2.40)mm3 ,control group (39.05 ±2.05)mm3, t=2.36, P＜0.05) while the right ones did not. On 6th week, the right ones began to reduce significantly ( model group ( 37.85 ± 2.11 ) mm3, control group ( 39.44 ± 2.10 ) mm3, t = 2.07, P ＜ 0.05 ) while the left one still reduced, but the extent of the left's reduction was bigger than the right( left:15% ,right:8% ). And there was apparent correlation between the behavior and the reduction of hippocampal volumes. Conclusion The behavior and hippocampal volumes of rat depressive model changes dynamically,and there was a regularity of them.