The invention relates to a rotor blade of a wind power plant having two rotor blade half-shells (1, 21) with in each case a leading-edge periphery and a trailing-edge periphery (8a, 22a), which rotor blade half-shells are adhesively fastened to each other along the leading-edge and trailing-edge peripheries (8a, 22) and which in case have a trailing-edge girder (3, 25), and each of the trailing-edge girders (3, 25) at least in certain sections is of rectangular design in a cross section along its longitudinal extent.