Metal chalcogenides are an attractive subject for investigation owing to their wide application in optoelectronics. Here, we report the discovery of a new cadmium-based quaternary sulfide, Na4CdGe2S7, with a wide band gap of 3.35 eV. The microscopic structure of this compound features two-dimensional [Ge2CdS7](infinity) layers, which were first found in metal sulfides. Remarkably, the Na/S ratio in Na4CdGe2S7 exceeds 50%, suggesting that it would have ecofriendly electrical applications, such as in sodium-ion-battery electrodes and fast ion conductors.