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 54 meter difference in the elevation of the source and the end of the river and it is 114 km long. The river drains a catchment area of 3140 km².