Abstract: By means of ion-exchange chromatograph and reverse phase HPLC,a new neurotoxin,named as Hainantoxin-Ⅴ (HNTX-Ⅴ),was isolated from the venom of the spider Seleconosmia hainana.The molecular weight of HNTX-Ⅴ was 3 969.5 Da measured by MALDI-TOF mass analysis.Under whole-cell patch-clamp mode,HNTX-Ⅴ could inhibit the tetrodotoxin-sensitive (TTX-S) sodium currents while it had no significant effect on tetrodotoxin-resistant (TTX-R) ones on the dorsal root ganglion (DRG) neuron of adult rats.The inhibition of TTX-S sodium currents by HNTX-Ⅴ was concentrate-dependent with the IC50 value of 46.8 nmol/L.The toxin did not effect the active and inactive time course of currents and did not have the effect on the active threshold of sodium channels and the voltage of peak inward current either,indicating that HNTX-Ⅴ inhibited mammalian voltage-gated sodium channels through a novel mechanism distinct from other spider toxins such as δ-ACTXs.We suggested that HNTX-Ⅴ maybe target the site 1 of sodium channels in a similar manner to TTX,Saxitoxin and μ-conotoxins.