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 concentrations 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 similar to VC in concentration-dependant manner. CONCLUSIONS： SPK has obvious anti-oxidant activities in vitro.