In current paper, influence of tris-hydroxymethyl-aminomethane (tris) in simulated body fluid (SBF) on degradation behavior of pure magnesium is investigated using electrochemical tests as well as degradation measurement. Our results shows that tris mainly affects earlier degradation behavior of pure magnesium alloy. Iris and HCl used in preparation of SBF will form Tris-HCl which only lowers corrosion potential of magnesium slightly but accelerates degradation rates of pure magnesium by teens times. Consumption of OH- generated during magnesium dissolution by Tris-HCl progressively promotes transformation from Mg to Mg2+, which is the main reason for quite high degradation rate of pure magnesium in SBF. Pure magnesium is also more sensitive to pitting corrosion due to inclusion of Tris-HCl in SBF. This study deepens the understanding on degradation mechanism of biomedical magnesium alloys. (C) 2010 Elsevier B.V. All rights reserved.