Sri Lanka Railways S12 is a class of Diesel-electric multiple unit (DEMU) built for Sri Lanka Railways by China's CSR Corporation.

Seven of the S12 DMUs were ordered to strengthen long-distance travel on the Main line from Colombo to Badulla.

The steep slopes on the up-country portion of the Main Line is difficult to operate.

Prior to the S12, only a few classes of locomotives were capable of operating this line.

The locomotives were purchased under a USD 101 million credit line agreement with China.