Mechanical vibration causes lots of damage in automotive industry, machinery manufacturing and aerospace field. Noise control also causes much damage to human health. So it is of great significance to seek materials with high damping capacity to alleviate or eliminate mechanical vibration and noise. Pure Mg has the highest damping capacity among all of the commercial metal materials, but its low mechanical property impose restrictions on its pervasive application. Therefore, magnesium matrix composites reinforced with high mechanical property reinforcement can exhibit excellent damping capacity and mechanical property simultaneously, and this kind of material has attracted great attention and interest from researchers in recent years. A variety of preparation methods has been utilized to prepare magnesium matrix composites reinforced with different reinforcements. In situ reactive infiltration is a relatively new processing method to prepare metal matrix composites, which combines the advantages of in situ reaction synthesis and pressureless infiltration, and it has received increasing attention because of its cost-effectiveness, simplicity and high-efficiency, and near-net shaping capability. And by tailoring the relative density of preform, magnesium matrix composites with a high volume fraction of ceramic reinforcement can be obtained. In view of the poor wettability of B₄C/Mg system leading to low efficiency of composite, Ti particulates with high melting point and immiscible with magnesium was added. And (B₄C+Ti)/Mg and (B₄C+Ti)/AZ91D composites have been prepared successfully by in situ reactive infiltration method with high efficiency and low cost. Microstructure, phase composition and damping capacities of the as-fabricated composites were characterized and analyzed. Results showed that with increasing the preparation temperatures, the reaction between the starting materials is more complete, and the microstructure of (B₄C+Ti)/AZ91D composites tends to be interpenetrating networks from particle reinforced structure. The strain-dependent and temperature-dependent damping capacities of (B₄C+Ti)/Mg and (B₄C+Ti)/AZ91D composites improve gradually with the increase of strain amplitude and temperature respectively, and the dominant damping mechanisms are dislocation damping and interface damping.