Natural windbreaks such as trees are very efficient barriers to high velocity winds. The windbreaks exert drag force causing a net loss of momentum and thus disturb the characteristics of flow. The main factors which can affect the efficiency of the windbreaks are tree height, width, tree arrangement, porosity, etc. However, tree porosity which is strongly related to the windbreak drag is very difficult to establish. Recently, computational fluid dynamics (CFD) have been actively used to investigate wind flow characteristics around artificial and natural windbreaks such as trees. As a first step in the simulation, the CFD model had to be designed as a porous media because of the complexity of the physical structure. In this study, the results of wind tunnel test were introduced to find the porosity and aerodynamic resistance of a tree windbreak. Black pine tree (Pinus thunbergii), a typical tree windbreak in Korea was chosen as the experimental tree. With the main factors of wind velocity, static pressure, and density of the tree, the aerodynamic porosity as well as the resistance factor of the tree was found. The average porosity at varied tree density were found to be 0.91, 0. 69 and 0.42 for one, two and three trees, respectively. The resistance factors which can be equaled to the drag coefficient were 0.55, 0.82 and 1.08 for one, two and three trees, respectively. The determined aerodynamic porosity and windbreak drag will be used later as input data of CFD models. Moreover, the experimental procedure as well as the use of real tree in the wind tunnel experiment of finding the aerodynamic porosity and windbreak drag of various tree windbreaks was established through this study.