A foldable travelling case includes a case body and two support plates. The case body has a bottom base and a top base with two opposite first side walls and two opposite second walls. The first and second side walls are connected with a periphery of the bottom base to respectively define a fold line with the bottom base. The support plates each have a bottom side pivotally connected with one of the first side walls such that each support plate is leanable against one of the first side walls so as to support the first side walls at an extended position. When the support plates are pivotally moved away from the first side walls, the first and second side walls can be folded along the fold lines and rested on the bottom base to reduce the volume of the travelling case.