The present study was carried out on forty eight epididymis of sexually mature dogs to elucidate light microscope features and the presence of testosterone receptors inside epididymis in different seasons. Twenty four dogs aged 3 years were used during the periods from 1/2/2015-1/2/2016. The epididymis were carefully dissected from the testis after orchidectomy operations and fixed, dehydrated, clarified and embedded in paraffin. Sections were stained with hematoxylin and eosin and periodic acid schiff. As well as, paraffin embedded cytoimmunochemistry technique was used for detection of testosterone receptors. Muscular coats showed no significant differences during different seasons or among segments. Epithelial height, stereocilia length, total diameter and luminal diameters indicated presence of significant differences among segments and seasons. There were morphological changes in epithelial cells during seasons. The folding was noticed during winter only. Imunoreactivity of testosterone receptors were demonstrated during all seasons in all epididymal segments. The study concluded that there were seasonal variations in dogs' epididymis being highest reproductive activity during spring and lowest during summer.
