Two proteins G2a and G2b with molecular masses of approximately 24 kDa were isolated from Naja naja atra (Taiwan cobra) venom using sequential chromatography on gel filtration, ion-exchanger and reverse phase columns. The results of Edman degradation and mass analysis revealed that G2a is a cysteine-rich protein reported previously, and G2b is a novel polypeptide. CD spectra showed that the gross conformation of G2a and G2b notably differed. G2a exhibited an activity higher than that noted with G2b on inhibiting carbachol-induced muscle contraction. However, the two proteins weakly blocked muscle contraction evoked by K+. The observations that the two proteins exhibit the toxic activity in the concentration of micromolar range suggest that they are inherently weak toxins as other snake venom cysteine-rich proteins.