The extension is expected carry more than 70,000 passengers per day and takes the total length of the Silom Line to 14.5km.
Passengers will be able to travel free-of-charge over the new section of line until January 5.
Bang Wa will become an interchange in 2015 with the completion of the metro Blue Line, and a further six-station extension of the Silom Line from Bang Wa to Taling Chan is expected to open in 2019.
