In a letter sent to The Associated Press and other media, Breivik writes the hunger strike will continue until his demands are met or he dies.
Breivik's lawyer Tord Jordet confirmed the letter was authentic and said his client is waiting for a response from prison authorities before starting the hunger strike.
Breivik is serving a 21-year prison sentence, which can be extended when it expires, for killing 77 people in bomb and gun massacres in 2011.
Among his demands, Breivik wants communication restrictions lifted and improved air conditions. He wants the available PlayStation 2 console replaced by a modern version.