Canberra's Exhibition Park has been targeted.

The Amenduni Australian Olive Expo's grove holds 200 olive trees, all of which have been stripped of their fruits due to be harvested before the October display.

The Hunter Valley, NSW, has also been hit recently.

The ACT grove is surrounded by security fences, which are more than one-metre high and have barbed wire around the perimeter.

No-one on the grounds witnessed suspicious activity.

Expo organiser, John Forrest, said it is disappointing that all the trees have been stripped because this is the first year they would have been harvested.

He added that the data would have been used to obtain yield variety trial results.

"We were hoping that this first harvest would yield about 20 to 30 litres of extra virgin olive oil," Mr Forrest said.

"The Expo grove is used every year for exhibitors to demonstrate new equipment and techniques."

Mr Forrest said the olive theft would not damage the operation of the expo, which is to be held October 28 and 29.