The use of ultrasonic for accelerating the chemical and physical processes of wool has gained high importance. This study aims to develop a method for reducing the energy and material consumption and decreasing fiber damage. Ultrasonic equipment (20 kHz) was used for grafting chitosan to wool fabric. Experiments were carried out under different times and chitosan concentration. The results showed using this technique decreases the time required for grafting chitosan onto wool which is less than the other procedures. Differential scanning calorimetry, Fourier transform infra-red, and weight gain analyses provided evidence that chitosan was grafted onto the acylated wool through the formation of new covalent bonds in a short time. Scanning electron microscope was used to study the morphology of wool samples before and after modification. The dyeing of the chitosan grafted-acylated wool fabrics indicates higher dye ability and lower shrinkage compared to the acylated and raw wool samples. The findings of this study support the potential of using ultrasonic as a friendly environment method for grafting chitosan onto wool with enhanced dye ability and reduced shrinkage properties. The grafted samples showed good antibacterial properties against Staphylococcus aureus as gram-positive and Pseudomonas aeruginosa as gram negative bacteria. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013