Holothuria arenicola is the most important and abundant sea cucumber species in the Mediterranean Sea on the Egyptian coast. This work aimed to investigate the prophylactic and the curative effects of H. arenicola extract HaE (200mg/kg) on gastric mucosal damage following indomethacin and cold stress in healthy rats. Sixty-four rats were randomly divided into four main groups. Rats of the first group (8 rats/group) were administered distilled water orally (control group), rats of the second group (8 rats/group) were administered single oral dose of indomethacin (150mg/kg) and exposed to cold stress (4±1°C) for 30min to induce gastric ulcer (GU) model (ulcer group), rats of the third group, prophylactic group (24 rats/group) were treated with HaE and/or ranitidine (RAN) and then exposed to GU and rats of the fourth group, curative group (24 rats/group) were exposed firstly to GU and then treated with HaE and/or RAN. The results clearly indicate that pre-treatment with HaE and/or ranitidine significantly decreases the ulcer index, showing 72.50%, 53.11% and 80.56% ulceration inhibition, respectively. However, post-treatment with HaE and/or ranitidine significantly decreases the ulcer index, showing 51.66%, 62.41% and 67.78% ulceration inhibition, respectively. The results also showed that pre and post-treatment with HaE and/or RAN significantly decreased gastric malondialdehyde (MDA) level and enhanced reduced glutathione (GSH), catalase (CAT), glutathione-S-transferase (GST) and superoxide dismutase (SOD) levels. The results clearly indicate that pre-treatment with HaE is preferable.