The performance of a heat pipe depends on several factors, one of which is the nature of the wick structure. Optimization of heat pipe performance requires wick structures that can provide high capillary pressure, and yet still offer low resistance to fluid flow. The current level of technology being developed in our laboratory makes it possible to engineer desired wick structures both micro- and macroscopically, especially tailored to optimize heat pipe performance. In order to assist the fabrication of unique wick structure, the influence of wick structure characteristics on heat pipe performance is numerically investigated in this work. Numerical methods are an effective toot to significantly reduce the number of experimental trials. Comparisons are made between performances of heat pipe with different wick structures; coarse pore sizes, fine pore sizes and a composite comprised of coarse and fine pore sizes. Results indicate superior performance, with a factor of up to 2, for heat pipe with composite structure combining coarse/fine wick. Validation of the simulation result presented using experimental data is being carried out. Copyright (c) 2005 John Wiley & Sons, Ltd.