Our aim was to determine the relationship between urban green spaces (UGS) number and greenness amount close to school with physical activity (PA) and body mass index (BMI) of adolescents. Participants (n = 194, aged 13–18 years) were recruited in 75 public secondary schools in the Porto Metropolitan Area. We used a self administered questionnaire to obtain information on height, weight, age and sex. PA levels were assessed using accelerometers. UGS number and greenness amount were measured using network buffers by 300, 500, 1000 and 1500 meters around each school, through geographic information system and normalized difference vegetation index (NDVI), respectively. Multilevel regressions were fitted to each green indicator individually. Multilevel models without adjustment showed a direct relationship between PA and NDVI [B = 118.14; 95%CI: 20.71, 215.57] and inverse relationship between PA and UGS number [B = -5.95; 95%CI: -10.06, -1.83] at 300 meters. Multilevel models with adjustment for socioeconomic deprivation showed a direct relationship between BMI and NDVI [B = 83.41; 95%CI: 30.84, 135.98] at 500 meters and a direct relationship between BMI and NDVI [B = 61.68; 95%CI: 3.07, 120.29] at 1000 meters. The present investigation does not support the idea that UGS number and the NDVI close to school promote PA and metabolic health in adolescents, as the results proved to be inconsistent and dependent on the distance threshold used to define geographic proximity.