OBJECTIVE:To study the anti-oxidative effects of spirulina kinase (SPK) in vitro. METHODS:The methods of phenanthroine-Fe2+ oxidation method,DPPH and auto-oxidation of pyrogallol were used to measure the effects of different concen-trations of SPK on scavenging hydroxyl (OH-) free radical,DPPH free radical and superoxide anion (O2-) free radical;IC50 of SPK was calculated. Prussian blue reaction was used to determine total reducing ability(by absorbance)of different concentrations of SPK to Fe3+. Vitamin C(VC)was used as positive control in above trials. RESULTS:SPK could eliminate the OH-free radical, DPPH free radical and O2- free radical in concentration-dependant manner,and the maximum elimination rate of SPK to OH- free radical and DPPH free radical were 86.82% and 78.98%(IC50 were 54.31,0.636 g/L),which were higher than VC (64.77%, 73.49%). The maximum elimination rate of SPK to O2- free radical was 78.31%(IC50 was 3.918 g/L),which was lower than VC (94.14%). In reducing ability test,SPK improved absorbance in reducing ability test system,and maximum absorbance was simi-lar to VC in concentration-dependant manner. CONCLUSIONS:SPK has obvious anti-oxidant activities in vitro.