en Experimental research article Experimental research article Introduction: Previous studies have shown that vitamin A and its derivatives such as retinoid and all-trans retinoic acid have a crucial role in memory, learning and synaptic plasticity. The receptors of vitamin A are seen in different parts of the brain such as hippocampus, where vitamin A has an important role in learning. In this study, the effect of intrahippocampal (CA1) injection of all – trans retinoic acid on spatial learning was investigated in adult male rats. Methods: 49 adult male rats divided in 7 groups were used. Test groups (1 – 4) received 1μl of all – trans retinoic acid dissolved in DMSO at concentrations of 1, 2, 4 and 8 μg/μl, for 4 consecutive days, 90 minutes before training. Group 5 received DMSO and 6th and 7th groups were designated as sham operation and control (intact) group, respectively. After each injection, Morris Water Maze (MWM) was used as a method to measure learning task. Results: This study showed that all – trans retinoic acid at the concentration of 1 μg/μl improved spatial learning in Morris Water Maze (p< 0.05). Conclusion: Our findings show that all – trans retinoic acid improves spatial learning in rats via enhancing the expression of learning related proteins. All – tran\'s retinoic acid; Spatial learning; Morris Water Maze; Hippocampus 60 67 http://ppj.phypha.ir/browse.php?a_code=A-10-88-4&slc_lang=en&sid=1 Mahmoud Aminizadeh 320031947532846003772 320031947532846003772 No Mehdi Abbasnejad mabbas@mail.uk.ac.ir 320031947532846003773 320031947532846003773 Yes Ahmad Ali Moazedi 320031947532846003774 320031947532846003774 No AhmadAli Papahn 320031947532846003775 320031947532846003775 No