Objective: To investigate the effects of a Pilates exercise program on disability, pain, lumbar mobility, flexibility and balance in patients with chronic non-specific low back pain. Design: Randomized controlled trial. Setting: University laboratory. Participants: A total of 54 patients with chronic non-specific low back pain. Intervention: Patients were randomly allocated to an experimental group ( n=27) included in a Pilates exercise program or to a control group ( n=27) receiving information in a form of a leaflet. Main outcome measures: Disability (Roland-Morris Disability Questionnaire and Oswestry Disability Index), current, average and pain at it least and at its worst (Visual Analogue Scales), lumbar mobility (modified Shober test), flexibility (finger-to-floor test) and balance (single limb stance test) were measured at baseline and after the intervention. Results: A between-group analysis showed significant differences in the intervention group compared to the control group for both disability scores, the Rolland-Morris questionnaire (mean change±standard deviation of 5.31±3.37 and 2.40±6.78 respectively and between-groups mean difference of 3.2 ± 4.12, p=0.003) and the Oswestry Disability Index ( p<0.001), current pain ( p=0.002) and pain at it least ( p=0.033), flexibility (0.032) and balance (0.043). Conclusions: An 8-week Pilates exercise program is effective in improving disability, pain, flexibility and balance in patients with chronic non-specific low back pain.