Inflammatory bowel diseases (IBD) are at the top of the worldwide rankings for gastrointestinal diseases as regards occurrence, yet efficient and side-effect-free treatments are currently unavailable. In the current study, we proposed a new concept for anti-inflammatory treatment based on gold (III) complexes. A new gold (III) complex TGS 121 was designed and screened in the in vitro studies using a mouse macrophage cell line, RAW264.7, and in vivo, in the dextran sulphate sodium (DSS)-induced mouse model of colitis. Physicochemical studies showed that TGS 121 was highly water-soluble; it was stable in water, blood, and lymph, and impervious to sunlight. In lipopolysaccharide (LPS)-stimulated RAW264.7 cells, the complex showed a potent anti-inflammatory profile, as evidenced in neutral red uptake and Griess tests. In the DSS-induced mouse model of colitis, the complex administered in two doses (1.68 μg/kg, intragastrically, and 16.8 μg/kg, intragastrically, once daily) produced a significant (* p < 0.05) anti-inflammatory effect, as shown by macroscopic score. The mechanism of action of TGS 121 was related to the enzymatic and non-enzymatic antioxidant system; moreover, TGS 121 induced changes in the tight junction complexes expression in the intestinal wall. This is the first study proving that gold (III) complexes may have therapeutic potential in the treatment of IBD.