A quick assembly pneumatic tool may be connected to a tool bit and has a housing, an anvil casing, a rear cover, an air inlet assembly, a rotor assembly and an impact assembly. The housing has a handle and a rotor casing. The rotor casing is formed on the handle and has a front chamber and a rear chamber. The anvil casing and rear cover respectively cover the front and rear chambers. The rotor assembly is mounted in the rear chamber and is selectively driven by the air inlet assembly. The impact assembly is mounted in the front chamber and the anvil casing and is selectively rotated by the rotor assembly. The separate rotor and anvil casings allow the rotor and impact assemblies to be inserted respectively in the front and rear chambers so that assembling the pneumatic is easy and quick.