Objective. - This study aimed to investigate associations between cardiorespiratory fitness (CRF) and lower limbs muscle power with mental health outcomes (depressive symptoms and powers and difficulties) in children from a middle-income country with one of the highest prevalence of depression globally. Methods. - Children and adolescents (aged 11-14 years) without from 10 public schools of four distinct geographical regions of Canoas city (Brazil) were invited to take part in the study. Physical fitness and mental health outcomes were assessed in a single visit. Physical fitness components assessed were CRF (multistage 20-m shuttle run test) and lower limbs muscle power (vertical jump). Mental health outcomes included the power and difficulties questionnaire (SDQ) and depressive symptoms (Patient Health Questionnaire-modified for Adolescents [PHQ-A]). Linear regression models, adjusted for relevant covariates, were performed. Results. - A total of 545 participants (52.5% female, mean age = 12.38 [1.2] years) were evaluated. A higher CRF was associated with lesser depressive symptoms (B = -0.15, 95%CI: -0.29; -0.01, P = 0.041) and emotional difficulties (B = -0.08, 95%CI: -0.16; -0.01, P = 0.030). A higher lower limbs muscle power was associated with lesser depressive symptoms (B = -0.07, 95%CI: -0.12; -0.02, P = 0.009). Conclusions. - The results support the notion that physical fitness is associated with lesser depressive symptoms in a middle-income country with one of the highest prevalence of depression globally. Further longitudinal studies are required to determine if physical fitness interventions are associated with a lower risk of incident depression in this age group. (c) 2024 Elsevier Masson SAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.