This laboratory study assessed the toxicological effects of ozone gas exposure on the terrestrial snail Theba pisana (Müller, 1774). Adult snails were exposed to different ozone concentrations for 30 min to evaluate mortality, changes in body weight, and histopathological alterations. Results showed that mortality and weight loss increased with higher ozone concentrations and longer exposure times, reaching 16.67, 20.00 and 53.33% mortality and 5.21, 7.34 and 8.43% weight loss percentages at 250, 500 and 1000 ppmv after 24 h post-exposure. Histopathological analysis revealed progressive damage in the digestive gland, ranging from mild destruction to complete rupture, along with degeneration and necrosis in foot tissues. These findings demonstrate that ozone induces pronounced toxic effects on T. pisana under laboratory conditions and provide baseline information on its biological and histopathological