Objective To observe the ultrastructure location of Huntingtin-associated protein 1（HAP1） in rat adrenal medulla and the effect of cold stress on the expression of HAP1 in rat adrenal medulla. Methods Fourteen healthy male Wistar rats were used in the present study and among them two rats were used for immune electron microscopy and twelve rats for cold stress experiment. In the cold stress experiment, animals were divided into control and cold groups randomly with six rats in each group. During the experiment, rats were housed in a room at the temperature of 4℃ for 12 hours and then immunohistochemistry and Western blotting were used to measure the expression of HAP1 in adrenal medulla. Results By using the immune electron microscopy, the results showed HAP1 was located on the external membrane of secretory vesicles of adrenal medulla and their membranous organelles. The expression of HAP1 in adrenal medulla of cold group significantly decreased as compared with that of control group (EM>P/EM><0.01). Conclusion HAP1 might be related with the adrenal medulla cells endocrine granula and involved in the transmission and release of adrenaline or noradrenaline in secreto