In this study we evaluated the composition of the crude extract and fractions of Tabernaemontana catharinensis (Apocynaceae) by HPLC/DAD and GC/MS. We also tested the antioxidant capacity and investigated the contents of polyphenols, flavonoids, tannins and alkaloids of T. catharinensis stem bark. The extract and fractions showed inhibition against thiobarbituric acid reactive species (TBARS), in the following order: ethyl acetate (IC 50 = 4.7 ± 0.2 μg/mL) > dichloromethane (23.9 ± 1.1 μg/mL) > n-butanolic (25.2 ± 0.4 μg/mL) > crude extract (38.0 ± 0.07 μg/mL). Moreover, the DPPH assay, presented IC 50 values ranged from 5.6 ± 0.6 to 30.3 ± 1.3 μg/mL. Contents of total phenols, flavonoids, tannins and alkaloids of T. catharinensis followed the order: ethyl acetate > n-butanolic > dichloromethane fractions > crude extract. HPLC/DAD analyses indicated that gallic, chlorogenic and caffeic acids, and rutin, quercetin and kaempferol are components of the species. Taken together, the results suggest that T. catharinensis could be considered an effective agent in the prevention of diseases associated with oxidative stress.