Ammonia is a weak base that can be used as a swelling agent on wool fibers before dyeing. In this study the pretreatment of wool with ammonia in different percent solutions (5, 10, 15, 20) is carried out, and its effect on dye-ability of wool by natural dyes such as madder, walnut shell, pomegranate peel, vine leaf, white and red onion skin, is analyzed. Also the effects of temperature, length of time, and concentration of ammonia on dye-ability of wool fibers were considered. Colorimetric data, and measurements of light and washing fastness were carried out, and the results of color change under ammonia treatment are reported.