Dyeing properties and fiber protective effects of two bifunctional reactive dyes, Rifafix Red BBN(C.1. No. ursavailable, dye I) and Rifafix Red 3BN(C.I. Reactive Red 241, dye II), on wool were investigated at various pH values. Dye I which has two solfonic groups showed the higher degrees of absorption and fixation than dye II which has four sulfonic groups. And dye II was more sensitive to pH values than dye 1. At lower pH values, the blocking of basic sites of wool chain by sulfonic groups had iuluence on the deuces of absorption and fixation only at higher dye concentration. But at higher pH values, the effects appeared at lower dye concentration. Alkali solubility of wool was reduced by dyeing with bifunctional reactive dyes to a greater extent than monofunctional reactive dye of similar structure. And the wool dyed with bifunctional dyes was increased in its thermal stability.