BACKGROUND: The Pilates method has been widely used to treat patients with chronic low back pain. Pilates exercises can be performed in 2 ways: by using specific equipment or without it (also known as mat Pilates). There are no studies, however, that have compared the effectiveness of mat Pilates with that of equipment-based Pilates. OBJECTIVE: The aim of this study was to compare the effectiveness of mat Pilates and equipment-based Pilates in patients with chronic nonspecific low back pain. DESIGN: A 2-arm randomized controlled trial with a blinded assessor was conducted. SETTING: The study was conducted at a private physical therapy clinic in Brazil. PATIENTS: Eighty-six patients with chronic nonspecific low back pain participated. INTERVENTION: The patients were randomly allocated to 1 of 2 groups: a mat Pilates group (n=43) and an equipment-based Pilates group (n=43). The participants in both groups attended 12 Pilates sessions over a period of 6 weeks. MEASUREMENTS: The primary outcomes were pain intensity and disability. The secondary outcomes were global perceived effect, patient's specific disability, and kinesiophobia. A blinded assessor evaluated the outcomes at baseline and 6 weeks and 6 months after randomization. RESULTS: After 6 months, there was a statistically significant difference for disability (mean difference=3.0 points, 95% confidence interval [CI]=0.6 to 5.4), specific disability (mean difference=-1.1 points, 95% CI=-2.0 to -0.1), and kinesiophobia (mean difference=4.9 points, 95% CI=1.6 to 8.2) in favor of equipment-based Pilates. No differences were found for the remaining outcomes. CONCLUSIONS: Equipment-based Pilates was superior to mat Pilates in the 6-month follow-up for the outcomes of disability and kinesiophobia. These benefits were not observed for pain intensity and global perceived effect in patients with chronic nonspecific low back pain.