Homogeneous distribution by adsorption is one of the key issues for application of microencapsulated materials to textiles. This study focused on production and characterization of poly(methyl methacrylate-co-acrylic acid)/n-eicosane microencapsulated phase change materials (MEPCMs) as textile thermal comfort additives with a functional outer surface. For this reason, methyl methacrylate was copolymerized with acrylic acid at three different ratios. The chemical structure, thermal energy storage properties, and thermal stability of microcapsules were investigated by FT-IR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis techniques, respectively. Microcapsules were found to have a thermal energy storage capacity of 50.9–90.9 J/g in the 31.74–36.30℃ temperature interval and they release between −88.4 and −40.2 J/g in the 33.88–35.59℃ temperature interval. Using a scanning electron microscope and a particle size instrument, the spherical morphology and particle size distribution of were determined for the microcapsules produced. The average particle sizes were 22.53 µm, 21.87 µm, and 11.73 µm for microcapsules with increasing amount of acrylic acid content. The microcapsules were thermally stable up to at least 120℃.