In this paper, we describe our recent work on metal matrix composites (MMCs) with submicron-size TiB2 and Al2O3 particulates that are synthesized in situ from Al-rich AI-Ti-B and Al-TiO2-B powder reactants by reactive sintering. Reaction sequences examined in the two different reactant systems are summarized, and some experimental results on elevated-temperature properties, i.e. thermal expansion, temperature dependence of dynamic tensile modulus and creep behavior, are shown and discussed from micromechanics-based viewpoints.