A pipe end is expanded by an expander tool (1) comprising a plurality of jaws (10), which are radially movable in relation to a center axis between a retracted position and expanded position. The jaws (10) when retracted are intended to be inserted into the pipe end. The jaws (10) have outer jaw surfaces which are intended for engagement with the inner surface of the pipe end and which lie adjacent to one another in the retracted position of the jaws (10). The tool (1) further comprises a piston (2) or a cone with a tapered end for moving the jaws (10) between said positions and means moving the piston (2) or the cone in a reciprocating manner in the axial direction for expanding the pipe end. The tool (1) further comprises support structures whereby the jaws (10) are supported in a circumferential direction in the expanded position. A method for expanding a pipe using such a tool is also disclosed.