The purpose of the current study was to examine immobilization stress-induced antioxidant defense changes and estimation of the antioxidant potential of pre and post stress treatment of aqueous garlic extract in rat's liver. For this purpose, male Albino Wistar rats were treated with aqueous garlic extract both pre and after 6 h of immobilization stress. Pro-oxidant status of rat liver was evaluated by determining the levels of reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS), aspartate aminotransferase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), glucose, uric acid and the activities of super oxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST). In response to 6 h of immobilization stress a significant rise in the level of above mentioned liver enzymes were recorded. However, SOD, CAT and GST enzymatic activities showed a sharp decline. The extract treatment before and after stress, almost reverted the activities of studied biochemical parameters towards their control values. Current study highlighted the antioxidant potential of garlic extracts. Based on our study, we recommend the use of garlic extract as nutritional supplement for combating oxidative stress induced damage.