A 40-year-old Aboriginal man has died after collapsing at a prison in Wooroloo, an hour east of Perth.

The Acacia Prison inmate was found on Friday but he could not be revived and was pronounced dead at hospital, the state's Department of Justice said in a statement on Saturday.

Police say there does not appear to be anything suspicious, but they are investigating and there will be an inquest given it is a death in custody.

The Department of Justice will also conduct an internal review.

Acacia Prison is privately run by Serco Australia.

AAP