INTRODUCTION: Aquatic exercise is one of the most popular supplementary treatments for children with neuro-motor impairment, especially for cerebral palsy (CP). As water reduces gravity force which increases postural stability, a child with CP exercises more easily in water than on land. OBJECTIVE: The aim of the study was to examine aquatic exercise effects on gross motor functioning, muscle tone and cardiorespiratory endurance in children with spastic CP. METHODS: The study included 19 children of both sexes, aged 6 to 12 years, with spastic CP. They were included in a 12-week aquatic exercise program, twice a week. Measurements of GMFM (gross motor function measurement), spasticity (MAS-Modified Ashworth Scale), heart rate (HR) and maximal oxygen consumption (VO2max) were carried out before and after treatment. The measurement results were compared before and after treatment. RESULTS: GMFM mean value before therapy was 80.2% and statistically it was significantly lower in comparison to the same value after therapy, which was 86.2% (p < 0.05). The level of spasticity was considerably decreased after therapy; the mean value before treatment was 3.21 according to MAS, and after treatment it was 1.95 (p < 0.001). After treatment there was a statistically significant improvement of cardiorespiratory indurance, i.e., there was a significant decrease in the mean value of HR and a significant increase of VO2max (p < 0.001). CONCLUSION: Aquatic exercise program can be useful in improving gross motor functioning, reducing spasticity and increasing cardiorespiratory endurance in children with spastic CP.