Superintendent Motarafi Ntepe said the Bloemfontein dog unit was tipped off that a police vehicle was about to load and transport dagga in the Ficksburg area.
"On Tuesday, about 00:30, 10km from Ficksburg, they noticed the police bakkie travelling towards Rosendal."
Ntepe said the driver of the bakkie sped off when he realised he had been spotted.
In uniform and on duty
The bakkie was chased for about 30km until it was found parked on the premises of Rosendal police station.
The driver, who was trying to run away, was stopped and the vehicle searched.
Three bags of dagga were found on the front seat and there were another 16 bags in the back.
Ntepe said the 23-year-old constable was in full uniform and on duty when he was arrested.
Free State police commissioner Amon Mashigo said: "This kind of corrupt police official does not have a place in the South African Police Service.
"We are not going to tolerate this kind of behaviour in the police service," he said. SAPA