CPS1, the rate-limiting enzyme that controls the first reaction of the urea cycle, is responsible for converting toxic ammonia into non-toxic urea in mammals. While disruption of the functions of CPS1 leads to elevated ammonia and nerve damage in the body, mainly manifested as urea cycle disorder. Moreover, accumulating evidence has recently revealed that CPS1 is involved in a variety of human diseases, including CPS1D, cardiovascular disease, cancers, and others. In particular, CPS1 expression varies among cancers, being overexpressed in some cancers and downregulated in others, suggesting that CPS1 may be a promising cancer therapeutic target. In addition, some small-molecule inhibitors of CPS1 have been reported, which have not been confirmed experimentally in malignancies, meaning their future role is far from certain. In this review, we describe the structure and function of CPS1, highlight its important roles in various human diseases, and further discuss the potential diagnostic and therapeutic implications of small molecule compounds targeting CPS1.