The　effect　of　carbon　nanotubes　(CNTs)　on　the　aging　behavior　of　Mg-9Al　matrix　composites　was　studied,　and　the　evolution　of　microstructures,　mechanical　properties　and　thermal　conductivity　of　composites　during　the　aging　treatment　were　discussed.　Results　show　that　the　addition　of　CNTs　increases　the　solid　solubility　of　Al　in　Mg　matrix　and　limited　the　migration　of　grain　boundaries　during　the　aging　process,　which　can　promote　the　formation　of　continuous　precipitated　phases　beta-Mg17Al12　in　CNTs/Mg-9Al　composites.　The　rod-shaped　continuous　precipitates　in　coherent　relationship　with　Mg　matrix　can　effectively　hinder　the　dislocation　movement,　which　can　improve　the　mechanical　properties　of　the　composites.　Besides,　the　reduction　of　solid　solution　Al　atoms　during　aging　process　and　the　addition　of　CNTs　can　improve　the　thermal　conductivity　of　the　composites.　The　property　evaluation　indicates　that　the　tensile　yield　strength,　ultimate　tensile　strength,　diffusivity　and　thermal　conductivity　of　peak-aged　0.4CNTs/Mg-9Al　composite　are　275　MPa,　369　MPa,　34.5　mm(2)/s　and　68.4　W/(mmiddotK)　respectively,　showing　17%,　23%,　43%　and　45%　increasing　in　comparison　with　those　of　Mg-9Al　before　aging.