The leaflets sent by a small group of activists gathered at the border are sure to infuriate the North, which views such actions as propaganda warfare. The leaflets contained messages opposing another hereditary power transfer in North Korea, as well as portraits of Kim Jong-il and heir Kim Jong-un. It wasn't immediately known if they mentioned Kim Jong-il's death.
North Korea has previously warned that it would fire at South Korea in response to such actions, and Wednesday's balloon launch comes at an extremely sensitive time for North Korea.
Many in Asia are worried over the possibility of a power struggle between Kim Jong-un and rivals in a country with a nuclear programme. But there have been no signs of unrest or discord in Pyongyang.
With the country in a 10-day period of official mourning, flags were flown at half-staff at all military units, factories, businesses, farms and public buildings. The streets of Pyongyang were quiet, but throngs of people gathered at landmarks honouring Kim.
Kim Jong-il died of a heart attack on Saturday caused by overwork and stress, according to North Korean media. He was 69 - although some experts question the official accounts of the date and place of his birth.
Kim's bier was decorated by a wreath from Kim Jong-un along with various medals and orders. The body was laid out in the Kumsusan Memorial Palace, a mausoleum where the embalmed body of Kim's father - national founder Kim Il Sung - has been on display in a glass sarcophagus since his death in 1994.
A state funeral is set for Dec 28 in Pyongyang, to be followed by a national memorial service the next day, according to state media. North Korean officials say they will not invite foreign delegations and will allow no entertainment during the mourning period.
Activists vowed to send more leaflets later on Wednesday.
