Objective: To estimate the risk of ozone concentration and hospitalizations for asthma. Method: This is an ecological time series, which included individuals from 0 to 10 years old who lived in Campo Grande, Mato Grosso do Sul (Brasil), from 2008 to 2010. The data on hospitalizations for asthma were obtained online from DATASUS website. Data from environment levels of ozone were obtained from Instituto de Física of UFMS and temperature and humidity from Centro de Monitoramento de Clima e Recursos Hídricos (CEMTEC). Gap designs were made from 0 to 6 days and analyzed by generalized additive Poisson’s regression model and its 95% confidence intervals. Results: There were 5850 admissions, presenting daily changes from 2 to 13. The relative risks and their respective confidence intervals were obtained for each parameter: ozone-RR 0.9965 (0.9467-1.0463); precipitation RR-0.9975 (0.9476-1.0474); RH RR-0.9948 (0.9450-1.0455); RR-speed winds 1.0036 (0.9535-1.0538) and RRtemperature 0.9679 (0.9195-1.0163). Conclusion: It was possible to identify association of ozone as in the same day of exposure as in the days ahead after the admissions. Thus, this study showed an association between ozone and hospitalizations for asthma in a medium-sized city.