Four Chinese nationals were arrested over two grow houses which held $2.5 million worth of drugs following a series of police raids in April this year.

The group, who were each charged with cultivating a commercial quantity of a controlled plant, appeared in the ACT Magistrates Court on Wednesday morning.

Police said they seized 800 cannabis plants and 17 kilograms of packaged cannabis from the houses as part of an investigation into cannabis supply in the Canberra region.

Facts tendered in court show they found 400 cannabis plants and uncovered a highly sophisticated hydroponic set up in one of the houses at Flynn.

They discovered heat lights, timers, blask hosing and exhaust fans in the bedroom, garage and several makeshift rooms.

One of the rooms could only be accessed by a trapdoor or a hidden sliding door built into the back of a cupboard.

Police also took bags of cannabis from the fridge and bedroom drawers, $2000 cash and more than 100 root balls found in a garbage bag.

They arrested Aifeng Zhang, 51, and Zhezhu Quan, 44, who were at the Huelin Circuit house at the time of the raids.

Investigations revealed Mr Quan's visa ran out in 2010 and Ms Zhang only had a visa for three days in 2004, police said.

Each entered a guilty plea, through a Mandarin interpreter, before Magistrate Bernadette Boss on Wednesday.

They did not apply for bail.

The pair are set to be sentenced in the ACT Supreme Court and will next appear on July 10.

Another two suspects, Manxin Jin, 51, and Chunsheng Li, 48, were charged in connection with an Evatt grow house.

Neither entered a plea on Wednesday, but Mr Li's defence lawyer indicated his client would plead guilty at a later date.

The two will face court again on July 16.