An outwardly rectifying chloride channel (ORCC) was characterized in acutely dissociated hippocampal CA1 pyramidal neurons of adult rat by using inside-out configuration of patch clamp. The channels were usually activated by a long-lasting and depolarizing voltage step. Average single channel conductance was (16.58±1.54) pS for membrane potential between －60 mV and 0 mV, and (40.92±3.17) pS between 0 mV and +60 mV in symmetrical 150 mmol/L NaCl solution (n=10). The channel open probability was voltage dependent (V_m=－60 mV，P_o=0.44±0.12；V_m=+60 mV，P_o=0.86±0.06, n=10). The reversal potential of the channel was (－4.17±1.84) mV in symmetrical Cl^－ concentration (150 mmol/L). When partially substituting Na-Gluconate for NaCl, the reversal potential shifted to (－34.23±4.86) mV (［Cl^－］_i/［Cl^－］_o=(30 mmol/L)/(150 mmol/L)). This shift indicates a high Cl^－ selectivity of the channel. Chloride channel blockers DIDS and SITS showed a reversible inhibiting effect on the channel activity. These results provide a report of an outwardly rectifying chloride channel (ORCC) in hippocampal CA1 pyramidal neurons of adult rat.