OSR

OSR may refer to:

Science and technology

 * Operational sex ratio, of reproductively available males to females
 * On-stack replacement, used by Jikes RVM, a Java virtual machine
 * Optical solar reflector, a radiator material for space craft
 * OEM Service Release, a Windows 95 distribution
 * Open-source robotics

Transportation

 * Leoš Janáček Airport Ostrava, in Czech Republic, IATA code OSR
 * Ontario Southland Railway, in Canada
 * Texas State Highway OSR, in the US

Other uses

 * Old School Renaissance, a movement within tabletop role-playing games
 * Owasippe Scout Reservation, a Boy Scout camp in Twin Lake, Michigan, U.S.
 * Orchestre de la Suisse Romande, a Swiss symphony orchestra
 * Operational Situation Reports, or Einsatzgruppen reports, dispatches of the Nazi death squads
 * Ohio State Reformatory, a historic US prison
 * Odessa Soviet Republic, a short-lived Soviet republic
 * Office of Strategic Research, a CIA intelligence analysis organization once headed by Richard Lehman
 * Oilseed rape, a widely cultivated grain crop
 * Overseas Service Ribbon, a US military award