Abstract: Biodegradable magnesium alloys as new biomedical implant materials have been extensively studied because of their notable biodegradability over traditional bio-inert metals. However, the extreme degradation rate of pure magnesium leads to the loss of its mechanical integrity before the tissue recovers completely. The solutions to this challenge are as follows: (1) purification, (2) alloying, (3) surface modification, and (4) biodegradable magnesium-matrix composites (BMMCs) synthesis. Owing to the tunability of mechanical properties, the adjustability of degradation rate, and the improvement of biocompatibility, BMMCs reinforced with bioactive reinforcements have promising applications as a new generation of biomedical implants. In this review, the processing methods, Mg matrix, and reinforcement phases of BMMCs are discussed. Moreover, the review comprehensively discusses various BMMCs synthesized thus far, aiming to show the governing aspects of the achieved mechanical properties, corrosion behavior, and biocompatibility. Finally, this paper also discusses the research direction and further development areas for these materials.