Acutely isolated rat hippocampal CA3 pyramidal neurons were irradiated with a semiconductor laser for wavelength 670 nm and power 5 mW. And properties of voltage-gated Na+ channel were studied using the whole-cell patch clamp technique. The experiment revealed that activation voltage and peak voltage of Na+ channel shifted towards more negative potentials in irradiating 5 min and the action of laser irradiation reached stabilization in 7 min. There was no effect on peak currents of Na+ channel using laser irradiation. The peak current density of control group and irradiation group were (－383.51 ± 26.93) pA/pF and (－368.36 ± 33.14) pA/pF respectively (n=8, P > 0.05). －40 mV activated threshold potential and －30 mV peak potential for control group respectively dropped to －60 mV and －40 mV after irradiating 7 min. The half-activation voltage and the slope factor of the activation curves of Na+ channel were also changed by the laser's exposure. The former changed from (－42.091 ± 1.537) mV to (54.971 ± 1.846) mV (n＝8, P < 0.01) and the latter form (1.529 ± 0.667) mV to (2.634 ± 0.519) mV (n=8, P < 0.05). The results show that activation properties of Na+ channel are influenced by laser irradiating hippocampal neurons. Thus, depolarizing process of action potential is affected. And further physiological functions of neurons are altered as a result of low level laser irradiation.