To enlarge the bandgap of Cu2SnS3 (CTS), Ag‐incorporating CTS thin films are successfully deposited by sulfurizing Ag‐Cu‐Sn precursors featuring various Ag contents and the constant Cu/Sn ratio of 1.75, which is the optimal value for CTS thin‐film solar cells. To control the Ag content of the films, the thickness of the Ag layers of the precursors is varied from 0 to 200 nm, which corresponds to the Ag/(Ag + Cu) ratio of the films varying from 0 to 0.32. The films featuring Ag/(Ag + Cu) ratios smaller than 0.16 are solid solutions of CTS and Ag2SnS3, that is, (Cu,Ag)2SnS3 (CATS), while the film featuring the Ag/(Ag + Cu) ratio of 0.32 appears to be a mixture of CATS and Ag‐Sn‐S related crystals, such as Ag8SnS6. The grain size and bandgap increase as the Ag/(Ag + Cu) ratio increases up to 0.16. The highest power conversion efficiency (PCE) of 3.6% is obtained for the cell featuring the Ag/(Ag + Cu) ratio of 0.08. The highest open cell voltage (VOC) for the CATS thin‐film solar cells is obtained to be 0.284 mV. However, the improvement in PCE is attributed to the increase in the short‐circuit current density and fill factor of the cell rather than the increase in VOC.