Hainantoxin-��(HNTX-��) is a novel antagonist of tetrodotoxin-sensitive sodium channels isolated from the Chinese bird spider Selenocosmia hainana Wang.The analysis of three dimensional structure of HNTX-��, solved by two dimensional nuclear magnetic resonance(2D NMR), reveals that it adopts an inhibitor cystine knot structural motif. To explore the relationship between structure and function of HNTX-��, the solid-phase chemical synthesis of R26A-HNTX-�� and K27A-HNTX-��, two mutants of HNTX-��, where Arg-26 or Lys-27 was substituted with Ala, was carried out using the Fmoc chemistry on the Pioneer Peptide Synthesizer System. The synthetic peptides were purified and then oxidatively refolded under the optimal conditions. The synthetic mutants were analyzed by MALDI-TOF mass spectrometry for molecular weight. The conformation of oxidative refolding of mutants were determined by NMR spectroscopy. The results show that the mutants and native HNTX-�� have similar three dimensional structure. Using the whole-cell patch-clamp technique, R26A-HNTX-�� was demonstrated to inhibit tetrodotoxin-sensitive (TTX-S) sodium currents significantly and K27A-HNTX-�� failed to affect TTX-S sodium currents, indicating that Lys 27 but not Arg 26 is the key residue related to the bioactivity of HNTX-��.