Brasilsat B3 is a Brazilian communications satellite. It was launched on 4 February 1998 by an Ariane 44LP carrier rocket, as part of a dual-payload launch with Inmarsat-3 F5. It was built by Hughes Aircraft, based on the HS-376 satellite bus. It operates by Star One, a subsidiary of Embratel.

The Brasilsat B3 was launched to meet the great demand of the Brazilian market and to bring satellite communication to some cities in the Amazon Region, which still did not have access to satellite services, these locations were for the first time connected to Brazil, and the world. In addition, the B3 unveiled the Brasilsat B2, which has now been used in open or pay-TV broadcasts, telephone services, and data transmission.

The Inmarsat-3s were built by Lockheed Martin Astro Space (now Lockheed Martin Missiles & Space) of the USA, who were responsible for the basic spacecraft, and the European Matra Marconi Space (now Astrium), which developed the communications payload.

The Inmarsat I-3 communications payload can generate a global beam and a maximum of seven spotbeams. The spotbeams are directed as required to make extra communications capacity available in areas where demand from users is high.