Thousands of soldiers goose-stepped in parade in Seoul as the frail, stroke-crippled Kim Jong-il and his 27-year-old son, Kim Jong-un observed and saluted the troops, the South Korean Yonhap news agency reported.
The celebration marked the 65th anniversary of the founding of the ruling Workers' Party.
Kim Jong-il, 68, assumed leadership of the country following the death of his father and last month appointed his son to the military rank of four-star general. Sunday's joint father-son appearance was seen as an introduction to the country's future leader, a Los Angeles Times correspondent reported from Seoul.
North Korea is a security concern for Western countries. Under Jong-il's leadership, the military conducted atomic weapons tests in 2006 and 2009.