An intake system for a horizontally opposed type internal combustion engine can contribute to an improvement in output performance without sacrificing the intrinsic merit of the horizontally opposed type internal combustion engine. Specifically, the intake system ensures that the overall height of the engine remains small. First and second intake ports are provided at head portions of first and second banks, which are arranged on the left and right sides. First and second intake distribution ports are arranged horizontally at a front wall of an intake surge tank 10, which is disposed on the rear end side of and adjacent to a crankshaft 1. The first and second intake ports are respectively connected with each other through first and second intake pipes disposed along a top surface or bottom surface of the engine E. Throttle valves for controlling intake quantities in the first and second intake pipes are provided in upstream portions of the intake pipes.