Microencapsulated phase change materials (MicroPCMs) were synthesized by in situ polymerization using melamine-formaldehyde (MF) resin as shell and n-octadecane as core. The employed MF prepolymer was prepared by incorporating formaldehyde once and melamine for three times. The effects of dropping rate of MF prepolymer on the surface morphology, dispersibility and thermal stability of the microcapsules were systematically investigated using scanning electronic microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSCP) and thermogravimetry analysis (TG). The results show that, with the dropping rate of the MF prepolymer decreasing, the flocculation phenomenon of microcapsules decreases and the globular surface becomes smoother; and the thermal stability increases regularly. The average diameter of the microcapsules is about 2.2 mu m and the diameter distribution is narrow. The enthalpy of the microcapsules containing 59 wt% n-octadecane is 144 J g(-1). In addition, the remnant formaldehyde content of the microcapsules is 68.6 mg kg(-1), which is highly attractive for the application of MicroPCMs. (c) 2007 Elsevier B.V. All rights reserved.