OAC or OAc may refer to:

• Ohio Arts Council
• Ohio Athletic Conference
• One America Committee
• Online Archive of California
• Ontario Academic Credit
• Ontario Access Coalition
• Ontario Agricultural College
• Ontario Arts Council
• Open Air Club, the University of Liverpool's hillwalking society
• Orthodox Anglican Church, a denomination of the Continuing Anglican movement in America, part of the Orthodox Anglican Communion.
• Orthodox Anglican Communion, a worldwide Continuing Anglican body of which the Orthodox Anglican Church is a part.
• Outdoor Adventure Club, an outdoors/extreme sports club at Auburn University, AL

Acetoxy group, abbreviated AcO or OAc, is a chemical functional group of the structure CH₃-C(=O)-O-. It differs from the acetyl group CH₃-C(=O)- by the presence of one additional oxygen atom. The name acetoxy is the short form of acetyl-oxy.