Officers executed search warrants at an industrial unit in Barry Docks and a property in the town on Tuesday.
They found 20 plants, drug growing equipment and cash.
The drugs and all equipment were seized.
A 41-year-old man from Barry has been arrested on suspicion of producing and released under investigation.
Detective Inspector Dean Taylor said: “We are committed to tackling drug issues in the area and anybody with information about drug dealing in the community should have the confidence to report it to us – they can call us via 101, or if they prefer, report it anonymously to Crimestoppers on 0800 555 111.”