This paper determines thermal properties of blends of polyvinyl alcohol (PVA)-stearic acid (SA) and polyvinyl chloride (PVC)-stearic acid (SA) as form-stable phase change material (PCM) for thermal energy storage (TES). In the blends, SA has a function of storing latent heat of fusion during its solid-liquid phase change when the polymer (PVC or PVA) as a supporting material prevents melted SA leakage because of its structural strength. Therefore, such blend is form-stable and can be used as PCM without encapsulation for passive solar TES applications. The maximum amount of SA in both composites found as high as 50 wt% without any seepage of SA in melted state. The dispersion of SA into the network of solid polymer matrix was investigated using an optical microscope (OM). The miscibility of SA with PVA and PVC were proved by Fourier Transfer Infrared (FT-IR) Spectroscopy method. Furthermore, melting temperatures of SA in PVA-SA and PVC-SA blends with form-stable mass combination (50 wt% polymer-50 wt% SA) and the total latent heats of fusion of the blends were found as 67.4 degrees C and 64.7 degrees C, and 132.68 and 129.34 J/g, respectively by Differential Scanning Calorimetry (DSC). Polymer-stearic acid blends as form-stable composite PCM were found to have great potential for especially solar space and building heating applications in terms of their satisfactory thermal properties and cost-effectivity.