The influence of the manganese-alloying on the structure and magnetocaloric properties of the Gd5Si2.05Ge1.95 compound was studied by X-ray powder diffraction and magnetization measurements. The Gd(5)Si(2.05-x)Ge(1.95-x)Ma(2x) (2x=0, 0.03 and 0.08) compounds crystallized in the Gd5Si2Ge2-type monoclinic structure. In all X-ray powder diffraction patterns, a minor hexagonal Gd5Si3 phase was observed as a second phase. With increasing Mn content, the unit cell volume increased. For the compounds with x=0, 0.03 and 0.08, the first order phase transition was observed. The maximum isothermal magnetic entropy change of the Gd5Si2.05-xGe1.95-xMn2x,compound with 2x=0.03 at 275 K was found to be -11.6 J/(kg.K) in an applied field of 5 T.