Objective To investigate the electrophysiological characteristics of neurons in developing visual cortex and to observe the reciprocal connection and the function of integration between adjacent neurons. Methods Whole cell recordings of the visual cortex from SD rats (4～28 d old) were obtained by using "blind" whole cell patch clamp recording technique. Bipolar stimulating electrodes were placed in the white border under the visual cortex. Postsynaptic currents(PSCs) were evoked by using stimulation of 0 1 Hz. Results There were three types of PSCs recorded in 156 cells in the first developmental month: irresponse, monosynaptic response and polysynaptic response. The incidence of polysynaptic PSCs increased from 12 36% before eye opening to 31 34% after eye opening ( P