ONJ

ONJ may refer to:


 * Olivia Newton-John (1948–2022), an English-born Australian singer and actress
 * osteonecrosis of the jaw, a severe bone disease that affects the maxilla and the mandible
 * Odate-Noshiro Airport (IATA airport code: ONJ), in Akita Prefecture, Japan
 * Onjob language (ISO 639 language code: onj)
 * Orchestre National de Jazz, a French jazz ensemble