The objective of this study was to investigate the influence of aggregate characteristics and gradation on the skid resistance of various asphalt mixtures. Asphalt mixture slabs with different combinations of aggregate sources and gradations were fabricated in the laboratory. These slabs were polished with a wheel-polishing device developed by the National Center for Asphalt Technology. The frictional characteristics of each slab were then measured by the sand patch method, British pendulum, dynamic friction tester, and circular texture meter. Aggregates used in these mixtures were characterized by petrographic analysis, conventional test methods (acid insolubility, magnesium soundness, Micro-Deval, and British polish value), and the aggregate imaging system (AIMS). In addition, the aggregate gradation of each mixture was described by the two-parameter cumulative Weibull distribution function. Statistical analysis of test results led to the development of a function for predicting the International Friction Index, which is a measure of skid resistance of asphalt mixtures, after different intervals of polishing. The parameters of this function were found to be related to ( a) initial and terminal aggregate texture measured by using AIMS, ( b) rate of change in aggregate texture measured by using AIMS after different polishing intervals in the Micro-Deval, and ( c) the Weibull distribution parameters describing aggregate gradation. This function can be useful for estimating the frictional characteristics of an asphalt mixture surface during the mixture design stage.