Spencer admitted during a seven-hour hearing at ACB headquarters he had taken Nandrolone to help his recovery from a back injury that had kept him out of cricket since 1994.
The 29-year-old tested positive in a random drugs control following Western Australia's Mercantile Mutual Cup One-day final defeat to New South Wales in Sydney in February.
The ACB's anti-doping committee, chaired by Justice William Gerard of the Victorian State Supreme Court and including Dr Susan White of the Australian Sports Drug Medical Advisory Committee and Justice Glen Williams from the Queensland State Court of Appeal, spent seven hours hearing the case.
Spencer played six Limited-Over games for Western Australia last season.
He was born in England but moved to Australia as a five-year-old. He played two first class games for Kent in 1993 and four county games in 1994. He played for Western Australia in the same period until his back injury forced him out.
"No sport would be pleased that one of its players had been found guilty of this type of offence but I am reassured by the fact that this player was identified and dealt with quickly through the ACB's testing program and anti-doping procedures," ACB chief executive Malcolm Speed said after the hearing.
"This decision sends the clear message that cricket will not tolerate any player taking prohibited substances and will move swiftly to deal with any person found to have breached the ACB's anti-doping policy."
Nandrolone is an anabolic steroid used to boost muscles and to increase strength and power. It also speeds up recovery time after injury, allowing users to train harder.
Copyright AFP 2001
Australian paceman Spencer on steroid charge