OBJECTIVES: This study aimed to assess the effect of water- and land-based exercise on lung function in children with post-COVID-19 condition. METHODS: This was a randomised controlled trial with multigroup pre--post-test design. Children with post-COVID-19 condition aged 10-12 years were randomly assigned to water-based exercise (AQUA), land-based exercise (LAND) or a control group with no exercise (CONTROL). The outcomes were the changes in lung function (Lungtest Handy) from baseline to immediately after the 8-week intervention. Parameters measured included forced expiratory volume in 1 s (FEV), forced vital capacity (FVC) and vital capacity (VC). RESULTS: After the intervention, there was a significant difference (p<0.01) between the AQUA and LAND groups compared to the CONTROL group for FEV values ((2,64)=6.80; p=0.91; p<0.01, η2=0.18) and significant differences between the CONTROL and AQUA groups (p<0.01) and the CONTROL and LAND groups (p<0.05) for FEV ((2,64)=6.96; p=0.91; p<0.01, η=0.18). Repetitions-groups interactions for FEV/%FVC ((2,64)=0.71, p=0.162, p>0.05, η=0.030) showed that the changes that occurred varied from group to group and the reason for this was an upward trend in the LAND and AQUA groups and a downward trend in the CONTROL group. CONCLUSION: The study found that a supervised twice weekly 8-week exercise training programme in water and on land improved lung function in children with post-COVID-19 condition.