A neurotoxic peptide, named Hainantoxin-V (HNTX-V), was isolated from the venom of the Chinese bird spider Selenocosmia hainana. The complete amino acid sequence of HNTX-V has been determined by Edman degradation and found to contain 35 amino acid residues with three disulfide bonds. Under whole-cell patch-clamp mode, HNTX-V was proved to inhibit the tetrodotoxin-sensitive (TTX-S) sodium currents while it had no any effects on tetrodotoxin-resistant (TTX-R) sodium currents on adult rat dorsal root ganglion neurons. The inhibition of TTX-S sodium currents by HNTX-V was tested to be concentrate-dependent with the IC(50) value of 42.3nM. It did not affect the activation and inactivation kinetics of currents and did not have the effect on the active threshold of sodium channels and the voltage of peak inward currents. However, 100nM HNTX-V caused a 7.7mV hyperpolarizing shift in the voltage midpoint of steady-state sodium channel inactivation. The results indicated that HNTX-V inhibited mammalian voltage-gated sodium channels through a novel mechanism distinct from other spider toxins such as delta-ACTXs, micro -agatoxins I-VI which bind to receptor site three to slow the inactivation kinetics of sodium currents.