To study the separate and combined effects of environment, lifestyle, physical characteristics, blood biomarkers and genetic factors on aetiology of major chronic diseases in adult Chinese. China Kadoorie Biobank (CKB) is a large blood-based prospective cohort study. The baseline survey took place in 5 urban and 5 rural areas across China during 2004-2008, with collection of data through questionnaire, physical examination and blood samples. Following the baseline survey, 5% of the randomly selected participants were surveyed in 2008, and repeated every 4-5 years. All participants would be followed for cause-specific mortality and morbidity through registries and for any hospital admission through linkages with health insurance databases. Overall, 512 891 adults aged 30-79 years (mean 51.5) were recruited, including 41.0% men and 55.9% from rural areas. Blood collection was successfully done in 99.98% of the participants. The prevalence of current regular smoking was 61.3% in men and 2.4% in women. The prevalence of regular alcohol consumption (i.e., weekly) was 33.4% in men and 2.1% in women. At the baseline, 41.8% of men and 45.3% of women were overweight or obese (i.e., BMI≥24.0 kg/m2) and 32.2% of men and 30.2% of women were hypertensive (i.e., SBP≥140 mm Hg or DBP≥90 mm Hg). For each of the main baseline variables, there were large variations on age, sex and areas of study. CKB seemed to be a powerful and rich resource in studying the environmental and genetic determinants of major chronic diseases in the Chinese population.