Biodegradable microcapsules entrapping an activated carbon impregnated with potassium nitrate were prepared by the solvent evaporation method in a (solid/oil/water) complex emulsion system. Biodegradable poly-epsilon-caprolactone (PCL) was used as a wall material. The effects of the PCL concentration and the weight fraction of the activated carbon on the morphology of the microcapsules prepared and the entrapment efficiency of potassium nitrate were investigated. On increasing the PCL concentration, the surface of the microcapsules became smoother, the voids formed inside decreased, and the fraction of potassium nitrate entrapped in the microcapsules increased. The entrapment also increased with the weight fraction of the activated carbon and reached a constant value at 2.5 wt%. By using the activated carbon impregnated with potassium nitrate as a core material, the amount of potassium nitrate entrapped in the microcapsules increased, and relatively high entrapment efficiency was maintained.