Phase change materials (PCMs) have wide application areas in solar energy storage systems due to their large thermal storage capacity. In this study, stearic acid (SA)/silicon dioxide (SiO2) nanocapsules were synthesized using a sol-gel method. SiO2 was used as the shell material, and SA was selected as the energy storage material. The surface morphology, chemical structure, crystalloid phase, phase change properties and thermal stability of the nanocapsules were observed by Field emission scanning electron microscopy (FESEM), Fourier transformation infrared spectroscope (FT-IR), X-ray diffraction (XRD), Differential scanning calorimeter (DSC) and Thermo gravimetric Analysis (TG), respectively. The results of FESEM show that the nanocapsules present regular spherical, and the diameter increased with increasing ammonia-to-ethanol ratio. The analysis from T-IR and XRD indicates that the nanocapsules are composed of SA and amorphous silica by physical interactions. Besides, the nanocapsules have good energy storage capacity and thermal stability from the results of DSC and TG test, since the latent heats of which reached as high as 169.4 J/g and decreased only 5.2 J/g after 3000 thermal cycles. Due to the excellent thermal properties, the SA/SiO2 nanocapsules developed in this work have great potential in solar energy storage and can be chosen as a candidate in solar heating systems.