The dependence of Tb and Co concentration on the magnetoresistance (MR) of TbFeCo amorphous films with perpendicular magnetic anisotropy have been studied at room temperature. TbxFe(88-x-y)Coy films (where x=15--37 at% and y=5--25 at%) with thickness of 200 nm are deposited by dc-magnetron sputtering. The MR ratio is sensitively dependent on the Tb concentration. The MR ratio is increased up to about 2.8% for a Tb concentration of about 22.4 at% then decreased for more Tb content. No significant effect of Co concentration on the MR ratio has been observed. The relation between MR ratio and film composition can be ascribed to the dependence of the domain wall width on the film concentration. The domain wall width decreases with an increase in Tb concentration and again increases for more Tb content showing its minimum value at about 22.4 at % of Tb concentration. It may be considered that the observed MR is contributed from the domain wall.