Markers of oxidative stress in the hepatopancreas and carotenoid and vitamin E content in the carapace of the invasive crab Percnon gibbesi and the native crab Pachygrapsus marmoratus were compared as indicators of their physiological condition and environmental adaptation. Crabs similar in size were collected from coastal waters of Portals Vells (Mallorca Island, Spain; 39°28’18.79”N, 2°28’19.63”E) at <1 m depth. Vitamin E levels were significantly higher in P. marmoratus than in P. gibbesi, whereas all carotenoid concentrations, except astaxanthin, were significantly higher in P. gibbesi. Catalase, glutathione peroxidase and glutathione reductase activities were significantly greater in P. marmoratus. Malondialdehyde concentration, a marker of lipid peroxidation, was higher in the hepatopancreas of P. gibbesi. The differences in carotenoid and vitamin E contents and in the antioxidant enzyme activities are a reflection of the different physiological activity of the two species and may suggest that P. gibbesi is not a potential competitor for the native crab P. marmoratus.