Bovine Serum Albumin (also known as BSA or "Fraction V") is a serum albumin protein derived from bovine blood. The BSA protein is purified and fractionated through a certain heat-shock procedure, followed by extensive diafiltration and ion-exchange to remove other plasma proteins, lipids, and extraneous ions.

BSA has numerous biochemical applications including ELISAs (Enzyme-Linked Immunosorbent Assay), immunoblots, and immunohistochemistry. It is also used as a stabilizer and cell growth supplement in cell and microbial cultures. Further applications include, e.g., for serum-free cell culture, as additive for hybridoma cell culture, protein stabilizer, and blocking agent.