Thermal energy storage systems provide several alternatives for efficient energy use and energy conservation. Microcapsules of natural coco, fatty acid mixture were prepared to be used as phase change materials for thermal energy storage. The coacervation technique was used for the microencapsulation process. Several alternatives for the capsule wall material were tried. The microcapsules were characterized according to their geometric profiles, phase transition temperatures, mean particle sizes, chemical stabilities, and their thermal cycling. The diameters of microcapsules prepared in this study were about 1 mm. Coco fatty acid mixtures have kept their geometrical profiles even after 50 thermal cycles for melting and freezing operations in temperature range from 22 to 34 degrees C. It was found that gelatin + gum Arabic mixture was the best wall material for microencapsulating coco, fatty acid mixtures. Copyright (c) 2005 John Wiley & Sons, Ltd.