The present work included biological studies, morphological and anatomical features, beside histological and ultrastructural alternations due to effects of the botanical thymol, as poison bait, on the digestive gland of the Egyptian giant garden slug, Limax maximus (Family: Limacidae) after treating it with LC₅₀ and LC₉₀ for 48 hrs.Thymol is considered as a botanic molluscicidal mono-terpenoid, that is found in several plants. The estimated value of LC₅₀ and LC₉₀ of thymol are 269.77 and 362.79 ppm respectively. The effect of LC₉₀ on the digestive gland caused severe histological changes and ultrastructural abnormalities; as: cytoplasmic vacuolation, scattered toxic agents, degeneration of some nuclei and cells, rupture of microvilli, increasing of calcium spherules inside secretory cells and wide-fused vacuoles. So, thymol may be of great value in the field to control the target slug, as safe and economic molluscicide, which no harm upon ecosystems instead of using chemical pesticides that could pollute the environment