Public open spaces (POS) enable many leisure activities. However, few studies have evaluated how different exposures to POS with structured physical activities (PA) could affect the leisure-time PA (LTPA) of adults with chronic diseases. This study aimed to analyze the associations between different exposures to POS and LTPA in adults in primary health care in Brazil. In 2019, a cross-sectional study was conducted with a representative sample of 615 users of 15 Basic Health Units in São José dos Pinhais. The POS exposure was measured by the presence and distance (GIS), and the usage and frequency of usage were self-reported. The IPAQ identified walking and moderate-to-vigorous PA (MVPA). Data were analyzed with multilevel Poisson regression adjusted for the possible confounders (sex, age, economic level, chronic diseases). The prevalence of walking and MVPA ≥150 min/week was 12% and 14%, respectively. The usage of POS increased by 52% the likelihood of walking ≥10 min/week (PR: 1.52; 95%CI: 1.02–2.21), while usage ≥2 times/week increased by 2 times the likelihood of this outcome (PR: 2.01; 95%CI: 1.28–3.05). The usage of POS increased by 2.7 times the likelihood of MVPA ≥10 min/week (PR: 2.73; 95%CI: 1.86–3.97), and usage ≥2 times/week increased by 3.5 times the likelihood of this outcome (PR: 3.45; 95%CI: 2.14–5.42). Finally, the usage of POS increased by 3 times the likelihood of MVPA ≥150 min/week (PR: 3.03; 95%CI: 1.92–4.74), while usage ≥2 times/week increased by 3.8 times the likelihood of this outcome (PR: 3.81; 95%CI: 2.19–6.38). In conclusion, only the usage of POS is positively associated with walking and MVPA in the leisure time of adult primary health care users.