The river Loimijoki is a river in Finland and the longest tributary of the river Kokemäenjoki. The river originates at the lake Pyhäjärvi in Tammela and joins the river Kokemäenjoki in Huittinen. There is a difference in elevation between the source and the mouth of the river, which is long. The river drains a catchment area of . The river has several dams at Forssa, Jokioinen and Loimaa.
