Attorney-General Jarrod Bleijie says he is appealing the sentence handed down to Brett Peter Cowan, because he wants to take a tough stance on the "worst of the worst" child sex offenders.

Mr Bleijie announced today that the life sentence with a non-parole period of 20 years was "manifestly inadequate" for Daniel Morcombe's killer.

Cowan was last Friday sentenced by Justice Roslyn Atkinson for the abduction and murder of the 13-year-old in 2003.

Mr Bleijie said he had instructed the Director of Public Prosecutions to appeal the sentence, following discussions with Daniel's parents, Bruce and Denise Morcombe.