A mild method for the preparation of tryptanthrin and its derivatives by copper(I) catalysis with two identical isatins in the presence of KHCO₃ as a base is described. Furthermore, more complicated tryptanthrin derivatives are obtained in two steps with two different isatins in one pot. This work features readily available starting materials, mild reaction conditions, simple operation, good functional group tolerance, high yields and selectivity. This transformation not only provided a new method to access tryptanthrin and its derivatives, but also enriched the chemistry of isatins and copper catalysis.