This systematic review examined papers published in Korean, English and newer publications that were not included in previous studies to assess the effect size of aquatic exercise-based interventions on pain, quality of life and joint dysfunction among patients with osteoarthritis. Six national and international databases were used to review literature (published up to 7 March 2019) on randomized controlled trials of aquatic exercise-based interventions in patients with osteoarthritis. For the 20 studies included, a meta-analysis showed that aquatic exercise produces 0.61-point reduction (n = 756; mean difference (MD) = -0.61; 95% confidence interval (CI): -0.90--0.32) in pain compared with a control group, and aquatic exercise was effective in reducing pain (n = 315; MD = -0.28; 95% CI: -0.50--0.05) compared with a land-based exercise group. Another meta-analysis showed that aquatic exercise produces 0.77-point improvement in quality of life (n = 279; MD = -0.77; 95% CI: -1.38--0.15) compared with a control group. Finally, a meta-analysis showed that aquatic exercise produces 0.34-point reduction in joint dysfunction (n = 279; MD = -0.77; 95% CI: -1.38--0.15) compared with a control group. For patients with osteoarthritis, aquatic-exercise-based interventions are effective for reducing pain and joint dysfunction and improving quality of life.