PET fabrics were cationized via photografting under continuous UV irradiation with a cationic monomer. The grafted PET was dyed with three acid dyes. Effect of dye concentration, dyeing time, temperature and pH on acidic dyeing of the cationized PET fabrics was assessed to find optimal dyeing condition. The cationized fabrics was successfully dyed at $75^{circ}C$ under pH 5.5. However the dyeing sites of the grafted fabrics were nearly occupied above 5%owf dye concentration and the rapid exhaustion of the anionic dyes was observed. The dyeability of the cationized PET fabrics was increased proportionally with increasing percent grafting because of the introduction of ionic attraction between quaternary ammonium groups and acid dyes. Lower dyeability both at alkaline and pH 3 condition attributed to negative zeta potentials of the grafted fabrics and the reduced charge of the acid dyes respectively.