Abstract： Objective To observe the characters of EPSC-IPSC induced by paired-pulse stimulation of rat visual cortex layer Ⅱ / Ⅲ pyramidal neurons during critical period of visual development,and discuss their relationships,to discuss the role of short-term synaptic plasticity in the critical period of visual development of rats.Methods Thirty Wistar rats were used,they were divided into P10-P12,P14-P16,P21-P23,P28-P30,P35-P37 five groups,n =6.Whole-cell voltage clamp recording was performed,the membrane potential was clamped on -50 mV,0 mV respectively to separate EPSC and IPSC.We set the PPR as the observation indicator,analyzed the developmental features of EPSC and IPSC induced by pairedpulse stimulation of different groups.Results The PPR of layer Ⅱ/Ⅲ pyramidal neurons in group P10-P12,P14-P16,P21-P23,P28-P30,P35-P37 was 0.43 ±0.08,0.07 ±0.08,0.10 ±0.10,0.20 ±0.07,0.22 ± 0.12 respectively.The PPR of group P14-P16 decreased,the difference was statistically significant compared with the group before eyes open (t =- 3.13,P =0.04 ).The PPR of corresponding groups was 0.6036 ± 0.3021,0.2830 ± 0.0504,0.0287 ± 0.0907,- 0.0449 ± 0.1443, - 0.3089 ± 0.05553 respectively(F =5.0799,P =0.0037),the PPR of IPSC gradually reduced with age,and turned negative from the P28-P30 group,changed from PPF to PPD.Conclusions The PPR of EPSC response to visual stimuli rapidly,but did not change significantly in the critical period of visual development (P19 -P32).The short-term depression of IPSC increased gradually from the eyes open to the end of the critical period of visual development,which may play a more important role in the process of layer Ⅱ / Ⅲ pyramidal neurons maturation and the critical period of visual development ending.