Background Overweight and obesity are important risk factors for non-communicable diseases (NCDs) such as cardiovascular diseases (CVD), type 2 diabetes and certain cancers. NCDs are responsible for an increased number of deaths worldwide, including in developing countries. We aimed to determine the prevalence of overweight and obesity among youth and adults in a peri-urban area of Maputo city, Mozambique, and to assess their social and behavioral determinants. Methods A cross-sectional study was conducted in a Health and Demographic Surveillance System (HDSS) area in Maputo city. We measured BMI and interviewed 15-64-year-old inhabitants to assess sociodemographic and behavioral characteristics using the STEPwise Approach methodology. A household wealth index was derived through Principal Component Analysis of various household assets and physical activity (PA) was measured using pedometers and accelerometers. Univariable and multivariable analyses were conducted to determine associations between overweight/obesity and social and behavioral determinants. Results Among a total of 931 participants, the prevalence of overweight (BMI\geq25 kg/m2) and obesity (BMI\geq30 kg/m2) was 30.9% (95% confidence interval (CI) = 28.0, 33.9) and 12.6% (95% CI = 10.4, 14.7), respectively; one in every 10 youths and adults were underweight. Being female, older and living in a wealthier household were found to be significantly associated with overweight and obesity. Those with higher levels of education were found to have a reduced risk of being obese compared to those with no or lower levels of education. Behavioral risk factors (diet, alcohol and tobacco consumption and physical activity) did not significantly increase the risk of overweight and obesity. Conclusions Overweight and obesity are highly prevalent in this peri-urban part of the Mozambican capital, where underweight is still present in youth and adults, confirming that the country is facing a double burden of malnutrition. Social determinants of health should be taken into consideration in the design and implementation of NCD prevention programs.