The epididymis is a narrow, tightly-coiled tube that connects the efferent ducts from the rear of each testicle to its vas deferens in the male reproductive system. It forms in crescent-shape and attaches closely at the upper and posterior margins of the testicle. The epididymis is made up of three main regions: the head (Caput), the body (Corpus), and the tail (Cauda). The head of the epididymis is the widest and most superior region which receives spermatozoa from testis via the efferent ducts. Sperms are dilute in this region. Inferior to the head is the body region, which descends along the posterior edge of the testis and keeps slightly narrower in diameter than the head. The tail is the most distal part of epididymis joining with the vas deferens. The epididymis keeps an essential role in maturing sperms as well as storing them before they enter the vas deferens. Some infections or other disorders in epididymis would affect the production of normal sperms thus leading to infertility in male. Some target proteins on epididymis have been found for detecting of relevant diseases.