Documents were seized during searches on March 9 of homes around the Sydney suburbs of Hoxton Park and Bankstown and prisoners' cells in the Goulburn maximum security jail in southern New South Wales.
The raids follow the arrests of nine men in November over an alleged plot to bomb major targets in Sydney.
"There were no further arrests made but a number of items, including documents, were seized," a spokesman said.
Police and agents from the main spy agency ASIO are still examining the documents, he said.
Police said the raids were part of ongoing investigations linked to the arrests in November of nine Muslim men in Sydney and another nine in Melbourne on terrorism-related charges.
The men are accused of plotting major terrorist attacks, although no specific targets have been mentioned.
Some of the arrested suspects are detained in the maximum security wing at Goulburn prison.