The bioactivity of alkali treated TLM (Ti-25Nb-3Zr-2Sn-3Mo) alloy was evaluated by the simulated body fluid (SBF) soaking method. Sodium titanate (niobate) gel layer was formed on the TLM alloy after alkali treatment, and the gel layer thickness was increased with higher alkali concentration. After soaking in SBF for 43 h, only a small quantity of apatite nucleus were formed on alkali treated pure titanium, while Ca8H2(PO4)6·5H2O crystals were detected and there were more apatite nucleus on the alkali treated TLM alloy. Results show that the alkali treated TLM alloy has thicker sodium titanate (niobate) gel layer and consequently possesses higher bioactivity than the alkali treated pure titanium.