The main goal was to analyze the physical activity levels and the intention to be physically active differences between both countries regarding the gender, course and socioeconomic status. The sample was 3,052 adolescents (14.58 +/- 1.39 years), 1,516 males and 1,536 females. From the whole participants, 734 were Chilean and 2,318 Spanish. Physical activity levels were measured using the "International Physical Activity Questionnaire-Short Form" (IPAQ-SF), the intention to be physically active using the "Intention to be Physically Active" scale and the socioeconomic status using the "Family Affluence Scale II" (FASII). There are significant differences in physical activity levels and the intention to be physically active between both countries according to the gender (p <.001), course (p <.001) and socioeconomic status (p <.01). Data were higher in Spain than Chile. Moreover, the relation between these sociodemographic variables with physical activity levels and the intention to be physically active were different regarding the country. As the relation between these sociodemographic variables with physical activity levels and the intention to be physically active is different according to the country, cross-cultural researches are required to develop physical activity and health interventions adapted to people's needs.