Peptic ulcers (PU) are sores or lesions in the gastrointestinal mucosa extending throughout the muscularis mucosae, typically characterized by different stages of necrosis, neutrophil infiltration, blood flow reduction, increased oxidative stress and inflammation. Peptic ulcer is the disease that is associated with wound in the muscular mucous layer of the stomach. Sargassum wightii is a brown seaweed that contains bioactive components including fucoidan and fucoxanthin as well as large amounts of polyphenols and is used by locals for the treatment of peptic ulcer. The objective of this study was to evaluate the phytochemical and anti-ulcer properties of aqueous crude extract of Sargassum wightii using a rat ulcer model. Antiulcer activity was performed by analysing the content of total protein, sialic acid, fucose, hexose, glycoproetein, lipid peroxidation, catalase and superoxide dismutase enzymes in gastric juice and by histopathology studies on stomach tissue after treatment. The results showed that 500 mg/kg of the seaweed extract showed good anti-ulcer activity as compared with the standard drug (20 mg/kg Omeprazole). Thus, the present work validates the use of Sargassum wightii for gastric ulcer treatment.