In this study, the thermal performance of bio-inspired wick is investigated. In the first chapter, the capillary limit of bio-inspired wick is considered. The capillary flows in the wicks are visualized using a high speed camera. From the experiments, it is shown that the capillary performances of bio-inspired wicks are significantly higher than those of conventional mono-porous wicks. In the bio-inspired wicks, three distinct capillary flow regimes are observed, depending on the ratio between particle and cluster sizes. A semi-analytic model for predicting the capillary performance of bio-inspired wicks is developed for each regime. The model prediction indicates that the cluster size should be 4-6 times larger than the particle size for an optimal capillary performance. In the second chapter, the boiling limit of bio-inspired wick is considered. In order to gain understanding of the boiling phenomena, the bubble movements in the wicks are visualized. Based on the visualization results, an analytic model for predicting the boiling limit of the bio-inspired wicks is developed. The model predicts the experimental data well, and indicates that the permeabilities of liquid and vapor are key parameters for determining the boiling limits of wicks. The bio-inspired wicks have much higher boiling limit than the mono-porous wicks, since they have much higher liquid/vapor permeabilities, by separating the flow paths of the phases. From the model, an optimal configuration of bio-inspired wick is found to be 4 < D/d < 6.