The contract is the second the company has signed within a month.
The latest deal is seen by many as a sign of recovery in the shipbuilding after a years-long slump, according to market analysts and company officials.
Under the agreement, the Dalian shipyard will start to deliver the carriers in 2013, the group said in a press release.
“Global shipbuilding is showing signs of turnaround, raising hopes for additional contracts,’’ said a company spokesman.
Demand for the latest container ships has recently increased.
Market research firm AXS Alphaliner has claimed that the order book for containerships spiked in October following a decline of 27 months.
The situation started to get better in June.
The researcher said it will take some time for the industry to return to normal levels and added that it expects further containership deals to be signed before the end of the year.
The STX shipyard is planning to expand its shipping portfolio from a heavy dependence on bulk and car carriers, Lee said.