An amateur radio satellite is an artificial satellite built and used by amateur radio operators. It forms part of the Amateur-satellite service. These satellites use amateur radio frequency allocations to facilitate communication between amateur radio stations.

Many amateur satellites receive an OSCAR designation, which is an acronym for Orbiting Satellite Carrying Amateur Radio. The designation is assigned by, an organization which promotes the development and launch of amateur radio satellites. Because of the prevalence of this designation, amateur radio satellites are often referred to as "OSCAR".

These satellites can be used "free of charge by licensed amateur radio operators" for voice (FMSSB) and data (AX.25, packet radio, APRS) communications. Currently, over 18 fully operational amateur radio satellites are in orbit. They may be designed to act as repeaters, as linear transponders, and as store and forward digital relays.

Amateur radio satellites have helped advance the science of satellite communications. Contributions include the launch of the first satellite voice transponder (OSCAR 3) and the development of highly advanced digital"store-and-forward" messaging transponder techniques.

The Amateur Radio Satellite community is very active in building satellites and in finding launch opportunities. Lists of functioning satellites need updating regularly, as new satellites are launched and older ones fail. Current information is published by AMSAT.