Hainantoxin-IV, a neutoxic peptide from the spider Selenocosimia hainana, was synthesized by solid-phase method with fluorenylmethyoxycarbonyl amino acids (Fmoc-AA). Reverse-phase HPLC was used to monitor the oxidative folding of synthetic Hainantoxin-IV under different reaction conditions in order to find optimal conditions for renaturation of synthetic Hainantoxin-IV. The best renaturation yield was received in 5 mmol/L GSH and 0.5 mmol/L GSSG at pH 8.0 in 0.1 mol/L Tris-HCl and 0.1 mol/L NaCl buffer. The renaturated Hainantoxin-IV was monitored with MALDI-TOF MS reverse-phase HPLC and isolated mouse phrenic nerve-diaphragm preparation.