Wool fibers pretreated with chitosan and nano chitosan and dyed with saffron red and yellow mixture as natural dye by using microwave heating method. The effect of chitosan and nano chitosan concentrations on color strength (K/S) was measured. The results indicated that, wool fibers pretreated with chitosan and nano chitosan recorded higher color strength than the untreated fibers. Fastness properties and the color yield of the dye on wool fibers were evaluated. The results indicated that color fastness to rubbing, washing and perspiration of all dyed wool fibers are excellent to good. The morphologies structure of the untreated and pretreated wool fibers were examined by scanning electron microscopy (SEM). The untreated wool fibers have a rough surface. The pretreated wool fibers were swelling compared to the untreated fibers. The diameter of the fibers increased and has smooth and even surfaces. The changes in the surface morphology due to the effect of pretreatment with chitosan and nanochitosan.The antimicrobial activity with some species of bacteria and fungi were tested. The results indicated that the pretreated fibers exhibit higher reduction percent than the untreated fibers.