This study assessed the reliability and internal consistency of scales measuring parental and peer support for physical activity in Chilean children and adolescents. A cross-sectional study was conducted with 160 youth from Viña del Mar, Chile. Parental support was measured using the Family Support for PA Scale, and peer support through the Friends Support for PA Scale. The Family Support for PA Scale showed satisfactory reliability (Cronbach’s alpha >0.70), with improvements in the second evaluation, except for girls. It also demonstrated strong internal consistency and moderate to high reliability for most questions. The Friends Support for PA Scale showed sufficient internal consistency, but reliability varied, ranging from low to moderate. In conclusion, both scales can be valuable tools for assessing social support for physical activity among Chilean youth.