Kim's body was wrapped in red cloth and placed in a glass coffin. It was surrounded by blossoms of his namesake flowers, red "kimjongilia."
Kim Jong Un, the former leader's youngest son and successor, visited the body with military and party officials.
Kim Jong Il died of a massive heart attack on Saturday caused by overwork and stress, according to the North's media.
His death raised acute concerns in the region over the possibility of a power struggle between the untested son and rivals, in a country pursuing nuclear weapons and known for its unpredictability and secrecy.
U.S. officials are hopeful there will be stability in the leadership transition.
"I think [Kim Jong Un] is not going to want to have anybody rock the boat, and I don't think he's going to rock the boat," said Donald Gregg, former U.S. ambassador to South Korea.
Kim Jong Il's funeral is expected to be held next Wednesday. The nation has declared a period of national mourning to last until the day after he's buried.
The Associated Press contributed to this report.