BACKGROUND: Surveillance of physical activity (PA) is essential for the development of health promotion initiatives. The aim of the present study was to examine the prevalence of PA and sedentary behaviour with respect to socio-demographic factors in Chile. METHODS: A representative sample of 5434 adults aged ≥15 years (59% women) who participated in the Chilean National Health Survey (2009-2010) were included. Socio-demographic data (age, sex, environment, education level, income level and smoking status) were collected for all participants. PA levels were assessed using the Global Physical Activity Questionnaire. RESULTS: 19.8% [95% CI: 18.1-21.6] of the Chilean population did not meet PA recommendations (≥600 MET min week(-1)). The prevalence of physical inactivity was higher in participants aged ≥65 years, compared with the youngest age groups and was higher in women than in men. However, it was lower for participants with high, compared with low, education or income levels. The overall prevalence of sedentary risk behaviour (spending >4 h sitting per day) was 35.9% [95% CI: 33.7- 38.2]. CONCLUSION: Physical inactivity correlates strongly with socio-demographic factors such as age, gender and educational level. Results identify social and economic groups to which future public health interventions should be aimed to increase PA in the Chilean population.