The secretive communist state's leader, 66, is believed to have suffered a stroke last month, but South Korean intelligence sources have said he is still in control of the country.
"We have obtained information that Kim can brush his teeth without help," a South Korean government official told Yonhap, on condition of anonymity.
He dismissed media reports that Kim is partially paralyzed or in a critical condition.
On Wednesday the North Korean leader's deputy, Kim Yong-nam, denied reports that the leader had collapsed, calling them a "conspiracy."
South Korean President Lee Myung-bak has told his government to prepare for any sudden change in North Korea's political situation.
Concern over Kim's health arose when he failed to appear at a military parade in Pyongyang marking the country's 60th anniversary on Tuesday.
Kim Jong-il has ruled North Korea since 1994, when he succeeded his late father Kim Il-sung, the communist state's founder. According to Soviet records, he was born in the Russian village of Vyatskoye near Khabarovsk, where his father commanded a military brigade in which Chinese and Korean exiles served.
