Dyeing properties of hydrophobic polypropylene fibers using cationic dyes were investigated to improve dyeability by electron beam irradiation and sulfonic acid incorporation. The color strength of irradiated polypropylene fibers was examined according to the dyeing conditions including pH of dyebath, absorbed doses, and introduction of functional group to fiber substrate. The best dyeing result was obtained when sulfonic acid group incorporated polypropylene fibers after electron beam irradiation were dyed with cationic dyes at alkaline conditions and 30$sim$75kGy irradiation ranges.