Indomethacin, an indole acetic acid derivative, is an NSAID commonly used to treat rheumatoid arthritis, osteoarthritis and intestinal arthritis, bursitis, tendonitis, traumatic synovitis and ankylosing spondylitis. However, the most well-known side effect of this drug is stomach ulcers. Therefore, indomethacin is often used to create an experimental model of gastric ulcer in rats. It has been reported that reactive oxygen species (ROS) and lipid peroxidation formation and glutathione reduction play an important role in the pathogenesis of indomethacin-induced gastric ulcer and these changes are responsible for oxidative damage in gastric mucosal cells. Alcoholic extract of Tarantula cubensis spider, a homeopathic remedy, accelerates healing in different wounds or ulcerated tissues. The aim of this study was to determine the effects of a single dose of indomethacin on the oxidant and antioxidant system in the gastric mucosa after 3 days and whether Tarantula cubensis alcoholic extract (TCAE) has a protective role against these effects of indomethacin by comparing with the effects of Lansoprazole used in ulcer treatment. In the study, rats were divided into 4 groups as control group, Indomethacin group (25 mg/kg indomethacin), Reference group (25 mg/kg indomethacin+30 mg/kg Lansoprazole), Ulcer group receiving Indomethacin + TCAE) (25 mg/kg indomethacin+200 µg/kg TCAE) (n=7). MDA, GSH, SOD, GPx and CAT levels were determined in the stomach tissue of rats 3 days after indomethacin administration. Although there was no statistically significant difference in MDA, GSH and GPx levels 3 days after indomethacin administration, results closer to the control group were obtained from the TCAE group. It was observed that 3 days after indomethacin administration, a significant adaptation against gastric damage developed in rat stomach tissues and gastric damage decreased. In parallel with the decrease in damage, oxidant parameters (MDA) decreased and antioxidant parameters (GSH, GPx, and SOD) increased.