The crosslinked poly(methylmethacrylate) (PMMA) heat sensitive color-developing nanocapsules were prepared by emulsion polymerization, in which leucocompound was used as a core material and methyl methacrylate and unsaturated hyperbranched poly(amide-ester) as wall-forming materials. The nanocapsules were characterized by Malvern particle size analysis, scanning electron microscopy, Fourier transform infrared spectrophotometry (FTIR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and densitometry. Triton X-100 was used as the emulsifier of emulsion polymerization. The effects of the emulsifier content on the particle size distribution and morphology of nanocapsules were discussed in detail. The FTIR analysis of leucocompound-containing nanocapsules demonstrated that leucocompound was successfully encapsulated in the crosslinked PMMA matrix. TGA results showed that the resultant nanocapsules had good thermal stabilities. The DSC analysis of the resultant nanocapsules indicated that the glass transition temperature of the nanocapsules was 117.9 A degrees C. The resultant nanocapsules had narrower particle size distribution, smoother surface, and higher heat sensitive color-developing density with the percentage weight of emulsifier being 0.6 wt%.