In this study the effect of reactive dyeing on chemical properties of wool was investigated. Dyes featuring two reactive groups or one bifunctional stoup applied to wool, and dyeing was carried out with or without ammonia aftertreatment. The purpose of this investigation was to test the effect of the number and position of reactive groups on fixation ratio, urea-bisulphite solubility(UBS) and swelling in formic acid, on the physical properties of dyed wool fabric. The main results obtained from this study were as follows: 1. Molecular size, configuration and number of reactive group afreet the exhaution ratio and fixation ratio of the dye. The highest fixation ratio was attained with Lanasol Red G which they possesses two reactive groups. 2. In the case of a-bromoacrylamide dye, the urea bisulphite solubility of the dyed wools indicated significant dependence on the amount of dye applied and the number of reactive groups in the dye used. These results suggest that crosslinking of the peptide chains by the dye with both bifunctional group occurs. 3. The wool dyed with bifunctional reactive dyes showed a slight improvement in tensile strength and breaking elongation compared to the blank-dyed fabrics. 4. In the case of alkali after-treatment of the reactive dyeing, the UBS and mechanical properties of wool clearly indicated that the reactive dyes protected fibres against alkali degradation. This is ascribed to the fact that the $varepsilon$-amino groups in the Iysine which are responsible for alkali degradation are partially blocked by reactive dyes.