An aftertreatment system for treatment of exhaust gases exiting an engine includes a first Selective Catalytic Reduction (SCR) device in fluid communication with the engine. The first SCR device receives the exhaust gases exiting the engine for reducing a first quantity of oxides of nitrogen (NOx) present in the exhaust gases. The aftertreatment system also includes an oxidation catalyst in fluid communication with the first SCR device. The oxidation catalyst receives the exhaust gases exiting the first SCR device for oxidizing ammonia present in the exhaust gases into a second quantity of NOx. The aftertreatment system further includes a second SCR device in fluid communication with the oxidation catalyst. The second SCR device receives the exhaust gases exiting the oxidation catalyst for reducing the second quantity of NOx.