This study examined isolated and combined associations of physical activity (PA) and sitting time (ST) with body mass index (BMI) among older Brazilian adults. We have analyzed baseline data of 8,177 participants aged 50 years and older from the Brazilian Longitudinal Study of Aging. Respondents were categorized into sufficient PA/low ST, sufficient PA/high ST, insufficient PA/low ST, or insufficient PA/high ST using the Short Version of International Physical Activity Questionnaire. Multinomial logistic regression analysis examined the associations of being underweight (BMI, <18 kg/m2), overweight (BMI, 25-29.9 kg/m2), and obese (BMI, ≥30 kg/m2) with PA and ST categories. High ST (≥165 min/day) was associated with overweight (odds ratio, 1.26; 95% confidence interval [1.11, 1.44]) and obesity (odds ratio, 1.43; 95% confidence interval [1.21, 1.70]). However, no association was observed between PA and BMI. Participants in the insufficient and sufficient PA/high ST categories were more likely to be obese after adjusting for sociodemographic and health condition. Our findings call for public health initiatives that consider reducing ST in older adults.