Metabolic syndrome (MetS) is a common health problem in developing countries. We aimed to assess the association between different aspects of physical activity and MetS in our country. A standardized international questionnaire (Global Physical Activity Questionnaire) recommended by the World Health Organization was used in the third national survey of risk factors of noncommunicable diseases (SuRFNCD-2007) to collect physical activity data from a nationally representative sample of Iranian adults. Physical activity was evaluated in 3 domains: work, commuting, and recreational activities. Both duration and intensity of activity were considered. Biochemical measurements were carried out, and MetS was defined by the International Diabetes Federation and the Adult Treatment Panel III criteria. The data collected from a total of 3296 individuals were analyzed. The national prevalence of MetS was estimated to be between 24% and 30%, depending on sex and the criteria used. The prevalence of MetS among individuals with high-, moderate-, and low-category activity was 18.7% ± 1.5%, 25.8% ± 2.0%, and 27.9% ± 2.0%, respectively (P < .001). These rates were 12.6% ± 1.6%, 26.0% ± 1.5%, and 34.1% ± 3.2% among individuals with vigorous activity, with nonvigorous activity, and without activity, respectively (P < .001). We demonstrated a significant linear association between the number of metabolic abnormalities and lower levels of various aspects of physical activity (total physical activity, duration of domain-specific activity, and duration of intensity-specific activity; P < .001 for all). Notably, the risk for MetS increased 1.28-fold with every 30-min/d reduction in vigorous-intensity activity (95% confidence interval = 1.15-1.42, P < .001). The results of the present study should be considered for future public health programs in Iran.