The morphology and structure of wax crystals is one of the most important factors influencing flow properties of waxy crude oils. The pour-point depressant (PPD) improved flow properties of waxy crude oil by modifying the morphology and structure of wax crystals, and this modification, i.e., the effectiveness of PPD, is greatly affected by the oil composition. There have been some investigations into how the oil composition effects the effectiveness of PPD. However, these studies were basically qualitative. The objective: of this study is to quantitatively reveal the relationship between the change induced by PPD beneficiation in the morphology and structure of wax crystals and the oil composition. PPD treatment was made on eight waxy crudes, and microscopic observations were performed on the morphology and structure of wax crystals before and after PPD beneficiation. The fractal dimension of the wax crystal microstructure, which was used to characterize the morphology and structure of wax crystals, was determined on the basis of the microscopic images of wax crystals. A total of 11 parameters of oil composition, which are thought to have influence on the effectiveness of PPD and the morphology and structure of wax crystals, were measured. Among them, 5 were determined to be the representative parameters of oil composition using the cluster analysis, i.e., the concentration of precipitated wax at the studied temperature, the average carbon number of wax, the viscosity of the liquid continuous phase at 60 degrees C, the wax content, and the content of resins and asphaltenes. Further, a correlation was developed using the multiple regression analysis between the fractal dimension change induced by PPD treatment and three representative parameters of oil composition, i.e., the concentration of precipitated wax at the studied temperature, the wax content, and the content of resins and asphaltenes. This helps to quantitatively understand the relationship between the oil composition and microstructure of wax crystals.