The blast occurred in Landhi area of country's biggest city. About five kilogrammes of explosives attached to a motorcycle were detonated when a Pakistan Rangers vehicle carrying 10 personnel was passing through the area.
Seven personnel were injured in the blast and one of them later succumbed to his injuries in hospital, a statement from the Rangers said.
Two of the personnel were in a critical condition, officials said.
Police and Rangers cordoned off the area and conducted a search operation.