Cotton fabrics were pretreated with whey protein isolate (WPI) to improve their dye ability toward a tannin-rich natural dye obtained from Xylocarpus granatum bark. Comprehensive studies were conducted on these fabrics assessing their dyea bility, color fastness, physical characteristics, and ultraviolet protection level. All dyed samples were reddish-brown with a significant enhancement in the sample color strength (K/S) being observed for the pretreated samples.