A series of microencapsulated phase change materials (MEPCMs) containing nanoalumina-reinforced n-dodecane (C-12) as core materials and modified carbon nanotubes (CNTs) reinforced melamine-formaldehyde (MF) resin as shell materials was synthesized successfully via in situ polymerization. The effects of CNTs and nanoalumina on the morphology/thermal performance of the MEPCMs were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), laser flash analyzer (LFA), and thermogravimetric analysis (TGA). The results indicated that adding CNTs or nanoalumina had little influence on the spherical structure of the MEPCMs, but the supercooling degree of MEPCMs was decreased obviously. The reinforced MEPCMs exhibited excellent thermal durability and distinguished cycling characteristics during the 100th thermal cycling test. It should be noted that the thermal conductivity of MEPCMs was improved distinctly and had a linear growth with the addition of CNTs. In particular, the thermal conductivity of the MEPCMs was improved by 380.8% with the incorporation of 3.3 wt % (0.5 g) CNTs. Furthermore, reinforced MEPCMs presented a superior thermal stability, and its decomposition temperature was increased by about 10 degrees C than that for MEPCMs without nanoparticles.