Alexandrium tamarene can produce paralytic shellfish poisoning (PSP) toxins that can selectively block the voltage-gated sodium channel of many excitable membranes. Here we report the effect of PSP toxins crudely extracted from A.tamarense, on Na+M1196current at motor nerve terminals and whole cell Motor nerve terminals experiments were performed on mouse triangularis stemi nerve-muscle preparations. Presynaptic currents were picked up with a microelectrode inserted into the subendothelial space of the superficial nerve bundle under visual control using a×400 magnification water immersion objective. Patch-clamp whole cell recording configuration was used to study the effects of PSP toxins on the voltage gated Na+ current of differentiated NG 108-15 cells. The results showed that the PSP toxins clearly inhibited the voltage-gated sodium current of the mouse motor nerve terminals and the whole NG 108-15 cell; and that the effects were partially reversible. A dose of 1.15 nmol/L ST Xeq. PSP toxins can reversibly inhibit the voltage-gated sodium current of the mouse motor nerve terminals; a dose of 4.60 nmol/L. STxeq. PSP toxins can reversibly inhibit the voltage-gated sodium current of the whole NG108-15 cell while no inhibition effect on potassium current was observed. At the same experiment conditions, the reversible inhibitions of our prepared PSP toxins were the same as that of the standard saxitoxin on sodium current of the mouse motor nerve terminals and the whole NG 108-15 cell.