The legislation passed with the support of 187 lawmakers, mostly governing party members who support President Moon Jae-in's policy of engagement with North Korea.
Outnumbered opposition lawmakers didn't attend the vote after their attempt at delaying the balloting with nonstop speeches was foiled by governing party lawmakers, who used their three-fifths super majority to halt the speeches in a separate vote.
It was the first time that South Korea's parliament has passed a bill formally banning civilians from floating anti-North Korea leaflets by balloon across the tense border. South Korea has previously banned such activities only during sensitive times, and has normally allowed activists to exercise their freedom of speech despite repeated protests from North Korea.
Activists and defectors from North Korea have for years used huge helium-filled balloons to carry leaflets criticizing North Korea's nuclear weapons program and human rights record, USB sticks with information about world news, and US dollars.
Observers say North Korean leader Kim Jong Un likely saw the leafleting as a threat to his absolute rule over his 25 million people, who mostly have little access to outside information.
Lawmakers aligned with Moon say the legislation is intended to avoid unnecessarily provoking North Korea, to ensure the safety of people who live near the border, and to secure stable relations with the North.
Opponents accuse Moon of sympathizing excessively with North Korea or yielding to North Korean threats over the leafleting.
“This is a law that will block the flow of South Korea's great values, the spirit of democracy, freedom and equality, to North Korea,” conservative opposition lawmaker Tae Yongho said during a 10-hour speech.
“It's a law aimed at joining hands with Kim Jong Un and leaving North Korean residents enslaved for good.” Tae was a senior North Korean diplomat in London before defecting to South Korea in 2016 and was elected to South Korea's parliament in April.
The bill will take effect three months after being promulgated by the government, which is regarded as a formality. A lawyers' group in Seoul earlier said it would file a constitutional appeal if the bill is passed.