Filling of the 3d band of the manganese in GdAl2−xMnxforx < 0.2

X-ray, magnetic, electrical resistivity and ESR studies of GdAl_2?xMn_x compounds were performed. The transition temperatures, effective mass, thermal broadening of resonance linewidth and g-factors were obtained. For low concentration of GdMn₂ in GdAl₂ up to 20%, Mn is nonmagnetic. Increasing of the effective mass and the thermal broadening linewidth ESR with increasing x can be explained by the presence of d-electrons.