Former Special Constable David Parkin resigned earlier this month.
Deputy Chief Constable Jason Hogg said the pictures found on Parkin's personal phone were 'abhorrent.'
It was seized and examined last July, and 'contained a number of extreme pornographic images.'
SC Parkin was based at Didcot police station and was arrested in September 2018 on suspicion of possessing extreme pornographic images.
He admitted three offences at Oxford Crown Court and was sentenced last month.
Parkin was given a two year community order and rehabilitation for 10 days, he was also ordered to complete a sexual behaviour programme, 120 hours unpaid work and to pay costs of £480.
Now, a misconduct hearing at Thames Valley Police HQ in Kidlington this week has found he breached the Standard of Professional Behaviour in respect of discreditable conduct.
The force says the ex Special Constable would have been dismissed, had he still been serving.
Parkin resigned from TVP on May 7th.
Deputy Chief Constable Jason Hogg, said: “Special Constable David Parkin committed criminal offences for which there can be no excuse.
"The images found on his phone during the course of the investigation are both illegal and abhorrent and there is no place within our force for someone who thinks being in possession of such images is acceptable.”