The ad-funded service is free to listen on a computer.
MySpace has unveiled an online music store that lets its US members listen for free but pay for downloads.
The ad-funded service lets MySpace members listen to streamed tracks on their PC for free and build up long playlists of their favourite tracks.
Users must buy a copy of a track from the music store of partner Amazon to enjoy it on a portable player.
The service hopes to cash in on the long-standing link between MySpace and new and established bands.
The service has been launched with backing from the big four music labels - Sony BMG, Universal, Warner and EMI - plus independent music group The Orchard.
The move is widely being seen as a snub to Apples' iTunes, which is the dominant player in the online music market.
It is known that record labels are frustrated with Apple's refusal to charge higher prices for more popular tracks. On Amazon's music store, which is only available in the US, tracks start at $0.79 (£0.42)
At launch MySpace Music only has a few thousand tracks available but said this will grow to many millions as the partner labels open up their archives to it.
All the tracks sold will be free of copyright protection mechanisms known as Digital Rights Management software.
News that MySpace was working on a music store leaked in April 2007 and the launch was delayed as negotiations with record label EMI dragged on.
It is estimated that about five million bands and artists have a profile page on MySpace and the site has helped launch the career of many up and coming musicians and help them stay in touch with fans.
As well as making cash from adverts running on the page through which people choose the music they listen to the service will also generate revenue from ringtones, concert tickets and merchandise.
"The big question is whether they can change their environment so people will want to do their shopping as well as their gossiping [at MySpace]," said James McQuivey, research analyst at Forrester.
Mr McQuivey doubted whether the site would become a big source of revenue for MySpace as studies suggest that people do not watch their computer when using it to stream music.
The opening of the store won criticism from Charles Caldas, head of independent rights body Merlin.
Mr Caldas said it was "incredibly disappointing" that the service launched without finalising a deal with the biggest independent labels and artists.
Merlin's members, which includes Koch, Beggars Group and Domino, have a 9% share of the US music market - roughly equivalent to EMI's market share.