The structure of GaMnAs nanowires (NW) with nominal Mn concentration of up to 7 at% was investigated by transmission electron microscopy. The (Ga,Mn)As NW were grown on epiready GaAs(001) n-type wafers by molecular beam epitaxy. The crystal structure of the NW was determined to be zinc-blende. NW with Mn concentrations lower than 5 at% grow along the 111 direction. NW with higher Mn concentrations grow along the 110 direction and reveal a branching structure. The main nanowire and branches grow along the 110 directions belonging to only one {111} plane.