In this work, Ti and Mg alloys were made into composites by using spark plasma sintering, in order to combine the high stiffness of Ti and biodegradability of Mg alloys. The effect of the content of Mg–3Zn alloy on the degradability was studied by using electrochemical corrosion, immersion in simulated body fluid and incubation of Saos-2 cells. The results show that Ti–Mg metal-metal composites (MMCs) exhibit low Young's modulus (31–48 GPa) and good yield strength (616.5–642.8 MPa). The modulus and strength both decrease with the content of Mg–3Zn alloy increasing. The electrochemical corrosion rates of Ti–Mg MMCs were much lower than that of monolithic Mg–3Zn alloys. After an immersion for 21 days, Ti matrix remained integrity and Mg phase dissolved in the solution, inducing the formation of apatite layer on the MMCs. The precipitation of apatite increased with the content of Mg–3Zn alloy increasing. In vitro study indicated that Ti–10Mg and Ti–20 Mg MMCs possessed good biocompatibility to Saos-2 cells, while the biocompatibility of Ti–30 Mg MMCs decreased slightly. In summary, Ti–Mg MMCs are promising implant materials with adjustable degradation rates and improved biocompatibility for orthopedic applications.