To provide an air-inlet structure of a motorcycle in which air-inlet ducts can be connected to an air box without providing through holes for allowing passage of the air-inlet ducts on the main frame or bending the air-inlet ducts to bypass a main frame. An engine is supported on a pair of left and right front frames that extend from a head pipe that supports a front wheel rearward and downward. An air box supplies air to the engine and is arranged above the engine. Air-inlet ducts introduce air to the air box and extend on the outer sides of the front frames in a fore-and-aft direction of a vehicle body to be connected to an air-inlet port of the air box at the back of the front frames.