Aldosterone synthase (or 18-hydroxylase) is a steroid hydroxylase cytochrome P450 oxidase enzyme involved in the generation of aldosterone.

This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. This protein is primarily expressed in the zona glomerulosa of the adrenal cortex. Within the cell, it localizes to the inner membrane of the mitochondria. The enzyme has steroid 18-hydroxylase activity to synthesize aldosterone and 18-oxocortisol as well as steroid 11 beta-hydroxylase activity. Mutations in this gene cause corticosterone methyl oxidase deficiency.