A series of paraffin /poly (methyl methacrylate) blends were prepared as new kinds of form-stable phase change materials by encapsulation of paraffin into PMMA. The blends were prepared at different mass fractions of paraffin. The form-stable paraffin /PMMA blends were characterized using optic microscopy (OM) and Fourier transform infrared (FT-IR) spectroscopy. Thermal characteristics were measured by using thermo gravimetric analysis （TGA） and differential scanning calorimetry (DSC) technique. On the basis of all results, it was concluded that paraffin is encapsulated by PMMA. The blends have good thermal properties and degrade in two distinguishable steps. They have good energy storage capacity and melt at 58-60 °C.The blends have different degrees of hydrophobic. These form-stable paraffin /PMMA blends have important potential for some practical latent heat thermal energy storage applications.