IMPORTANCE: In China, diabetes prevalence has increased substantially in recent decades, but there are no reliable estimates of the excess mortality currently associated with diabetes. OBJECTIVES: To assess the proportional excess mortality associated with diabetes and estimate the diabetes-related absolute excess mortality in rural and urban areas of China. DESIGN, SETTING, AND PARTICIPANTS: A 7-year nationwide prospective study of 512 869 adults aged 30 to 79 years from 10 (5 rural and 5 urban) regions in China, who were recruited between June 2004 and July 2008 and were followed up until January 2014. EXPOSURES: Diabetes (previously diagnosed or detected by screening) recorded at baseline. MAIN OUTCOMES AND MEASURES: All-cause and cause-specific mortality, collected through established death registries. Cox regression was used to estimate adjusted mortality rate ratio (RR) comparing individuals with diabetes vs those without diabetes at baseline. RESULTS: Among the 512 869 participants, the mean (SD) age was 51.5 (10.7) years, 59% (n = 302 618) were women, and 5.9% (n = 30 280) had diabetes (4.1% in rural areas, 8.1% in urban areas, 5.8% of men, 6.1% of women, 3.1% had been previously diagnosed, and 2.8% were detected by screening). During 3.64 million person-years of follow-up, there were 24 909 deaths, including 3384 among individuals with diabetes. Compared with adults without diabetes, individuals with diabetes had a significantly increased risk of all-cause mortality (1373 vs 646 deaths per 100 000; adjusted RR, 2.00 95% CI, 1.93-2.08), which was higher in rural areas than in urban areas (rural RR, 2.17 95% CI, 2.07-2.29; urban RR, 1.83 95% CI, 1.73-1.94). Presence of diabetes was associated with increased mortality from ischemic heart disease (3287 deaths; RR, 2.40 95% CI, 2.19-2.63), stroke (4444 deaths; RR, 1.98 95% CI, 1.81-2.17), chronic liver disease (481 deaths; RR, 2.32 95% CI, 1.76-3.06), infections (425 deaths; RR, 2.29 95% CI, 1.76-2.99), and cancer of the liver (1325 deaths; RR, 1.54 95% CI, 1.28-1.86), pancreas (357 deaths; RR, 1.84 95% CI, 1.35-2.51), female breast (217 deaths; RR, 1.84 95% CI, 1.24-2.74), and female reproductive system (210 deaths; RR, 1.81 95% CI, 1.20-2.74). For chronic kidney disease (365 deaths), the RR was higher in rural areas (18.69 95% CI, 14.22-24.57) than in urban areas (6.83 95% CI, 4.73-9.88). Among those with diabetes, 10% of all deaths (16% rural; 4% urban) were due to definite or probable diabetic ketoacidosis or coma (408 deaths). CONCLUSIONS AND RELEVANCE: Among adults in China, diabetes was associated with increased mortality from a range of cardiovascular and noncardiovascular diseases. Although diabetes was more common in urban areas, it was associated with greater excess mortality in rural areas.