To examine the potential association between body mass index (BMI) and activities of daily living (ADLs) and instrumental activities of daily living (IADLs) disabilities in a population-based sample of Chinese nonagenarians and centenarians.This study analyzed data obtained from a survey conducted in 870 elderly Chinese adults aged 90 years or older in Dujiangyan. The participants were divided into 4 groups according to the World Health Organization (WHO) Asia criteria of underweight, normal weight, overweight, and obesity in BMI (<18.5, 18.5-23.0, 23.0-25.0, ≥25.0 kg/m(2), respectively) and to BMI quartile (<16.8, 16.8-18.9, 18.9-21.1, ≥21.1 kg/m(2), respectively). The ADL and IADL disabilities were measured using the physical self-maintenance scale (PSMS) and IADL scale developed by Lawton and Brody, respectively.The participants included in the current statistical analyses were 233 men and 505 women. The mean age was 93.5 ± 3.2 years (ranging from 90 to 108 years). Using the WHO Asia criteria, the prevalence of underweight and obesity were 43.9% and 6.6%, respectively. In long-lived women, the prevalence of ADL and IADL disabilities was significantly higher in either the underweight group (39.4% and 72.9%, respectively) or the obesity group (38.1% and 77.7%, respectively) compared with the normal weight group (31.4% and 60.8%, respectively). After adjusting for relevant covariates, the underweight group and obesity group showed significantly increased odds ratios (ORs) for either ADL (1.5 and 1.8, respectively) or IADL disability (1.9 and 1.4, respectively). Similar results were found when using the BMI quartile. However, in long-lived men, no significant difference was found with respect to the prevalence of ADL or IADL disability and adjusted ORs among the different BMI groups.Among Chinese long-lived adults, the risk of ADL and IADL disability was higher for women with both extremely low and high BMIs, but this pattern was not found in men.