Renin is a key enzyme in the renin-angiotensin system (RAS) which controls the blood pressure and electrolyte balance. By numerous studies on RAS and structures of renin and prorenin, the determination of three-dimensional structure for renin has been thought to be important in the rational approach to the drug design for antihypertensives. Here, several investigations for the three-dimensional structure of human and mouse renins are reviewed. These papers showed that the active site cleft had a less open arrangement in renins than that in other aspartic proteinases, although the general topology of both renins were quite similar. They also described subsites of renins and others.