A motorcycle sidecar is provided which includes a wheel positioned a given distance from wheels of a motorcycle, a wheel supporting assembly supporting the wheel in a manner that enables the wheel to be rotated, and absorbing road shocks, a stabilizer assembly connecting between the wheel supporting assembly and a body of the motorcycle to enable the wheel supporting assembly to be leaned when the motorcycle is leaned, and a main body installed on the stabilizer assembly, for transporting a passenger or a thing. When the motorcycle is leaned to the right or left during driving, the wheel is leaned to the right or left at the same angle with the ground as the motorcycle. Thus, the motorcycle can be safely driven without reducing the speed to the considerable degree, when it goes around a curve.