A nanoparticle size disperse dye treated with ultrasound has been applied on polyester fabric without using a carrier. Various dyeing and process parameters used are studied in detail, such as K/S values, dye particle size, dye exposure to ultrasound waves, printing paste pH, steaming conditions of prints, morphological study using SEM and TEM of dye particles and fastness properties of the prints. The use of nanosized dye particles enormously improves the colour depth of the prints without the addition of extra chemicals to the printing paste.