A propeller system for a boat includes a housing adapted to be mounted to a stern of the boat and having a receiving chamber inside and waterway at the bottom side thereof, a propeller rotatably disposed in the waterway of the housing, a driving device mounted in the receiving chamber of the housing and having a driving member and a linking member pivotally coupled to the driving member, and a guide ring connected to the linking member of the driving device and located in the waterway of the housing in such a way that the guide ring surrounds the blades of the propeller and is pivotable relative to the propeller. Thus, the propelling system has the advantage of increasing the utilization of the internal space of the boat.