Children's health status is related to their physical activity levels. Active commuting is associated with higher physical activity and reduced risk of all-cause mortality, cardiovascular disease incidence, and diabetes. The objective of this research was to study the levels of physical activity and the commuting to school (active vs. passive) in Spanish nine-year-old children, analyzing the differences by gender and by the geographical environment where they live (rural or urban environment). Accelerometry was used for the measurement of physical activity: Sedentary time (min/day), vigorous physical activity (min/day), moderate to vigorous physical activity (min/day), intensity (counts/min), steps (number). The questionnaire of the European Youth Heart Study (EYHS) was used to determine the geographical environment (city/urban, residential area/outside city, rural/village) and the modes of transport (active: Walking and bicycle, passive: Car, motorcycle, public transport). A total of 455 Spanish nine-year-old children (247 girls and 208 boys) belonging to the EYHS participated in this study. The results showed that boys were significantly more physically active than girls (p ≤ 0.001). Results also showed that active commuting to school was positively correlated with the levels of physical activity (r = 0.324, p ≤ 0.001). The geographical environment influenced the way in which children went to school, being active commuting to school significantly (p ≤ 0.001) less frequent in those children who lived in a rural environment (22.4%) than in those who lived in the city (57.1%) or in a residential area (62.7%). As active commuting to school means increasing levels of physical activity in both sexes, strategies should be implemented in order to encourage active commuting to schools, contributing at the same time to better health and sustainability of future generations.Sustainability 2019, 11, 7104 2 of 10 activity levels. Despite the well-known benefits of physical activity, recent research has showed a decrease in the active commuting rates to and from school [9][10][11].An important issue which predicts active commuting to school is the distance from home to school. Recent research in Spain has stated that the threshold distance for walking to school was 875 m, 0.54 miles, in children, and it was higher among urban (1250 m, 0.78 miles) than rural participants (675 m, 0.42 miles) [12]. Moreover, there is some controversy as to how distance to school can play an important role to counteract sedentary behavior. Hinckson et al. [13] indicated that distance to school was an important factor related to physical activity levels, where 1 to 2 km from school together with active commuting could be useful to counteract children's sedentary behaviors. However, for physically active children, active commuting does not seem to be as relevant.Low traffic density and route safety are positively associated with active school travel, but also positive parental views on active commuting, as well as high level of social interactions...