Tannic-acid-templated mesoporous silica nanoparticles (TAMSNs), which were synthesized using a simple, environmentally friendly, cost-effective, and nonsurfactant-based template method, were developed as a matrix for stearic acid to fabricate a novel shape-stabilized phase change material (SA/TAMSN). The characterization results showed that stearic acid was fully adsorbed on the TAMSNs by physical adsorption and the TAMSNs had no effect on the crystal structure of stearic acid. According to the DSC results, although the TAMSNs had a confinement effect on the activity of the stearic acid molecules, the fusion and solidification enthalpies of SA/TAMSN could reach 108.8 J g⁻¹ and 114.1 J g⁻¹, respectively. Additionally, the TGA thermograms indicated that there was no apparent weight loss from 20 °C to 223 °C for SA/TAMSN, which demonstrated that SA/TAMSNs have excellent thermal stability. All of the results suggested that the TAMSNs could be used as a promising matrix candidate for the shape stabilization of stearic acid.