The objective was to provide an evidence-based, systematic assessment of the burden of cancer due to overweight/obesity and physical inactivity in China. This study evaluated the proportion of cancers of colon, rectum, pancreas, breast (postmenopausal), endometrium, and kidney attributable to overweight [30 kg/m(2) > body mass index (BMI) ≥ 25 kg/m(2))/obesity (BMI ≥ 30 kg/m(2)) and physical inactivity in China in 2005. Data of prevalence of overweight/obesity and lack of physical activity were derived from cross-sectional surveys among representative samples of Chinese population, and data of relative risks on cancers were derived from meta-analyses or large-scale studies from China and East Asian populations. The attributable fractions were calculated by combining both data of prevalence and relative risks. In China in 2005, 0.32% of cancer deaths and 0.65% of cancer cases were attributable to overweight and obesity combined. Lack of physical activity was responsible for 0.27% of cancer deaths and 0.39% of cancer cases. Future projections indicate that the contribution of overweight and obesity to the overall cancer burden will increase in the next decades. The largest increased attributable fractions will be for endometrial cancer. The increase in attributable fractions would be greater in men and in rural populations. Although the current burden of cancer associated with overweight/obesity and physical inactivity is still relatively small in China, it is expected to increase in the future.