This research work investigated the effect of magnesium micro-addition on the structure and mechanical properties of tin bronze (Cu-10%Sn alloy). The properties studied were tensile strength, percentage elongation using universal tensile machine (130812), impact strength using charpy machine (U1820) and hardness using Brinell hardness tester model B 3000(H). The specimens were prepared by doping 0.2 -1.0wt% of Mg into Cu-10%Sn alloy at interval of 0.2 percent. The specimens were prepared according to BS 131-240 standards. Microstructural analysis was carried out using optical metallurgical microscope (L2003A) and scanning electron microscope (LEGALMU 11). Results obtained revealed that tensile strength and hardness of the alloy increased with increase of magnesium content up to 1wt% respectively. Impact strength and percentage elongation on the other hand, decreased with increase in magnesium content. Microstructural analysis revealed α-Cu rich phase dendrites surrounded by intermetallic compound (δ-phase). δ-phase (Cu₃₁Sn₈) particles formed in the interdendtritic region of Cu-10%Sn-Mg alloys. The Cu-10%Sn alloy doped with micro-quantity of Mg proved to increase the hardness and tensile strength, while its ductility and impact strength were reduced and it is therefore recommended for low speed engineering applications such as rolling-mill bearing and internal combustion engines.