Magnetic critical behavior of Mn5Ge3 ribbons was investigated by dc magnetization measurements. The critical exponents were obtained by a modified Arrott plot technique and the Kouvel–Fisher method. Finally, β = 0.372 ± 0.003 and γ = 1.05 ± 0.01 were determined. The exponent δ = 3.88 ± 0.02 obtained from the magnetization isotherm of TC fulfills the Widom scaling relation δ = 1 + γ/β. Moreover, with these exponents, the magnetization curves collapse into two independent curves following a single equation around TC. These results confirm the reliability of the obtained critical exponents. However, this set of exponents belongs to none of the classical theoretical models. This phenomenon is probably caused by the anisotropy of the Mn ions.