A former chaplain at a private girls' school has taken the stand in the District Court in Perth and denied downloading child pornography from the internet.

Matthew O'Meara is on trial accused of possessing pornographic images and videos of young girls.

He was arrested in 2010 when he was the chaplain at Perth College in Mount Lawley.

The images were on two thumb drives; one was found in a colleague's classroom and the other in the pocket of O'Meara's trousers.

He testified he found the second thumb drive in a staff area of the chapel and had intended to take it to lost property but police arrived at the school to interview him.

O'Meara will continue his evidence on Tuesday.