Guided by Shulman, 1986 and Shulman, 1987 tripartate model of teacher expertise [subject matter knowledge (SMK), pedagogical content knowledge (PCK), and general pedagogical knowledge (GPK)], the present study examined 162 U.S. and Chinese 3rd grade mathematics teachers' expertise in teaching fractions. Results show that U.S. teachers lag significantly behind Chinese teachers in SMK (concepts, computations, and word problems) and in some areas of PCK (e.g., such as identifying important points of teaching the fraction concepts and how to ensure students' understanding). Although the Chinese teachers performed poorly in comparison to their U.S. counterparts on a test designed to measure GPK (e.g., psychological and educational theories and applications), its poor reliability calls these results into question. The implications of this study are discussed in terms of practical ideas for teacher training in the U.S. and China. (Contains 5 tables and 1 figure.)