The Brick Expo, which runs across the weekend, raises money for the paediatrics ward at the Canberra Hospital.
Chairman David Boddy said some of the pieces on display took immense amounts of work to create.
"We have moving trains, and great ball contraptions and really technical models," he said.
"Engineering pieces like the Golden Gate Bridge, which is 15 metres, which is quite a feat, it's just stuck together with Lego, there's no glue or nails or wire holding it up — down to just very clever use of parts.