Stigmasterol (also known as Wulzen anti-stiffness factor) is one of a group of plant sterols, or phytosterols, that include β-Sitosterol, Campesterol, Ergosterol (proVitamin D_{2), brassicasterol, δ-7-Stigmasterol and δ-7-Avenasterol, that are chemically similar to animal cholesterol. Phytosterols are insoluble in water but soluble in most organic solvents and contain one alcohol functional group.}

Stigmasterol is an unsaturated plant sterol occurring in the plant fats or oils of soybean, calabar bean, and rapeseed, and in a number of medicinal herbs, including the Chinese herbs Ophiopogon japonicus (Mai men dong), in Mirabilis jalapa and American Ginseng.

Stigmasterol is also found in various vegetables, legumes, nuts, seeds, and unpasteurized milk. Pasteurization will inactivate stigmasterol. Edible oils contains higher amount than vegetables. Phytosterols normally are broken down in the bile.

Stigmasterol is used as a precursor in the manufacture of semisynthetic progesterone, a valuable human hormone that plays an important physiological role in the regulatory and tissue rebuilding mechanisms related to estrogen effects, as well as acting as an intermediate in the biosynthesis of androgens, estrogens, and corticoids. It is also used as the precursor of Vitamin D₃

Research has indicated that stigmasterol may be useful in prevention of certain cancers, including ovarian, prostate, breast, and colon cancers. Studies have also indicated that a diet high in phytosterols may inhibit the absorption of cholesterol and lower serum cholesterol levels by competing for intestinal absorption. Studies with laboratory animals fed stigmasterol found that both cholesterol and sitosterol absorption decreased 23% and 30%, respectively, over a 6-week period. It also possesses potent antioxidant, hypoglycemic and thyroid inhibiting properties.