Ulcerative colitis (UC) is a high incidence disease worldwide and clinically presents as relapsing and incurable inflammation of the colon. Bilirubin (BR), a natural antioxidant with significant anti-colitic effects, is utilized in preclinical studies as an intestinal disease therapy. Due to their water-insolubility, the design of BR-based agents usually involves complicated chemosynthetic processes, introducing various uncertainties in BR development. After screening numerous materials, it is identified that chondroitin sulfate can efficiently mediate the construction of BR self-assembled nanomedicine (BSNM) via intermolecular hydrogen bonds between dense sulfate and carboxyl of chondroitin sulfate and imino groups of BR. BSNM exhibits pH sensitivity and reactive oxygen species responsiveness, enabling targeted delivery to the colon. After oral administration, BSNM significantly inhibits colonic fibrosis and apoptosis of colon and goblet cells; it also reduces the expression of inflammatory cytokines. Moreover, BSNM maintains the normal level of zonula occludens-1 and occludin to sustain the integrity of intestinal barrier, regulates the macrophage polarization from M1 to M2 type, and promotes the ecological recovery of intestinal flora. Collectively, the work provides a colon-targeted and transformable BSNM that is simple to prepare and is useful as an efficient targeted UC therapy.