OSJ

OSJ may refer to:


 * Optical Society of Japan, a professional organization of physicists
 * Officer of the Order of the Star of Jordan, a military decoration of Jordan
 * Officer of the Venerable Order of Saint John, an order of chivalry
 * San José Observatory, an astronomy observatory in Buenos Aires, Argentina
 * Orchestra of St John's, a UK orchestra
 * Oblates of St. Joseph, a Catholic religious institute
 * Old San Juan, the historic colonial district of San Juan, Puerto Rico