Nanocapsules containing polyaniline homodispersed in n-octadecane(n-Oct) were synthesized by free radical emulsion polymerization and in situ polymerization using poly(methyl methacrylate-co-allyl methacrylate)(P(MMA-co-AMA)) as a shell, in which polyaniline was used as the nucleating agent. Furthermore, the surface morphologies, crystallization properties, thermal stabilities, and crystallization process of nanoencapsulated phase change materials(NanoPCMs) were investigated using scanning electron microscopy(SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TG), and wide-angle X-ray diffraction(WAXD), respectively. The results showed that the addition of aniline as a monomer and polyaniline generated by in situ polymerization had little effect on the morphologies, particle sizes, encapsulation efficiencies, and crystallization process, but the heat resistance properties slightly decreased. Addition of 1.5 g of aniline effectively improved the supercooling crystallization behavior of the nanocapsule.