Recently, there has been an increasing interest in magnesium as biomaterials due to its similar elastic modulus, density and strength to that of human bone than other currently popularly used metallic biomaterials. However, the knowledge of its biocompatibility is lacking. This paper reports the results of testing the cytotoxicity, haemolysis and acute toxicity on untreated and treated magnesium samples. The results showed that no cytotoxicity was detected on untreated magnesium samples. However, samples of alkali-treated magnesium caused distinct morphological changes on cells with a reduction in cell number vs the control group. In haemolysis tests, untreated magnesium showed a haemolytic effect, whereas there was a small haemolytic effect (2.2%) on alkali heat-treated metal; this is less than the allowable 5%. Magnesium samples coated with an organic film show the lowest haemolytic effect. No acute toxicity was observed; no animal deaths occurred and we observed no obvious weight differences in untreated magnesium vs organic coated samples compared to the control group.