This brought the death toll in the blast to eight, said spokesman Sizwe Kupelo.
More than 40 people were injured in the explosion last month.
“Doctors are trying their best to help the victims, but unfortunately due to the nature of their injuries, we have lost some,” said Kupelo.
The man died on Monday from burn wounds suffered in the explosion at the Dora Nginza Hospital, in Port Elizabeth.
The explosion at Rolfe Laboratories sparked a fire that resulted in the evacuation of the building. The blast also damaged a part of the building.
Police have opened an arson docket.