South Korea's defense ministry said it began playing the messages at two spots along the border.
The propaganda criticizes the communist regime while encouraging North Koreans to defect to the democratic and capitalist South.
South Korea removed the speakers in 2004 after an agreement between Seoul and Pyongyang. But the South reinstalled them in 2010 after the North torpedoed the South Korean warship, Cheonan, killing 46 sailors.
The broadcast campaign isn't exactly an eye-for-an-eye retaliation as promised by the South Korean government, but Seoul's defense ministry says it's considered the most effective method for now. The ministry said the North fears psychological warfare - a tactic in which Pyongyang considers itself weak.
The North has said it would shoot down the loudspeakers if the South used them again. Seoul's defense ministry has boosted its defenses in case Pyongyang makes any moves against the speakers.
Song Ji-sun, Arirang News.