Abstract Background: Mechanical Low Back Pain (MLBP) is a major cause of illness and disability, especially in people of working age. Aim of Study: The study was conducted to compare be-tween the effect of aquatic exercise and land-based exercises on pain level, functional disability and lumbar Range of Motion (ROM) in subjects with Chronic Mechanical Low Back Pain (CMLBP). Material and Methods: Sixty patients with chronic me-chanical low back pain of both gender participated in the study: 17 male and 43 female between 25 and 40 years old. They were divided randomly and equally into two groups: A study group (A), in which patients received land based exercise program; and study group (B), in which patients received aquatic exercise program. Both groups received the treatment program for 50min, three times per week, for one month assessment of patients in each group for pain level, functional disability and lumbar range of motion before and after treatment. Results: There were statistically significant differences in all outcome measures in favor of the water exercises group (p < 0.001). In land exercise group, there were statistically significant differences regarding pain intensity, oswestry disability index, and lumbar flexion (p < 0.0001), except for extension, right and left side bending range of motion outcomes (p>0.05). However, there were statistically significant differ-ences regarding all outcome measure in water exercise group (p < 0.0001) when comparing the pre-treatment with post-treatment results. Conclusion: Aquatic therapy is effective in decreasing pain severity, level of functional disability and improved lumbar range of motion in patient with chronic mechanical low back pain than land-based exercise.