Protein fibers are attractive topics in the past decades. Among them, soybean protein fiber, the regenerated protein-base fiber, is very popular due to its luster, smooth surface, breathability, and comfort. In order to blend with wool and reach union dyeing, soybean protein fiber was first bleached due to its yellow appearance. Various bleaching processes were introduced in this paper. Reactive dyes for cellulose and for wool, such as Unisol or Megafix dyes, together with proper dyeing process were selected and compared. The results showed that one-time oxidation bleaching is confirmed as the bleaching process due to its compromise of high whiteness and bursting strength. It is unable to reach union dyeing for soybean protein fiber/wool fiber with Unisol or Megafix dyes respectively while it is feasible to reach union dyeing of soybean protein fiber/wool fiber dyeing with Unisol dyes followed by Megafix dyes.