At the stroke of midnight, Kim Jong-Un, accompanied by top military leaders, visited the Kumsusan Palace of the Sun in Pyongyang - the mausoleum holding the embalmed body of his grandfather, the North's official KCNA news agency said.
The similarly preserved body of Kim's father, Kim Jong-Il, whom he succeeded as leader in December 2011, is housed in the same building.
"Kim Jong-Un, together with other visitors, paid homage to Kim Il-Sung in the humblest reverence for him," KCNA reported.
The centenary of his birth in 2012 was marked by a major military parade and Kim Jong-Un's first public speech.
More From This Section
There were no indications of a similar parade being prepared today, but the South's Yonhap news agency cited officials as saying Pyongyang might be readying a symbolic show of military force.
"Artillery pieces including multiple rocket launches and self-propelled guns are being assembled near Pyongyang," it quoted an unidentified government official as saying.
In an address to top military, party and government leaders to mark today's holiday, the North's nominal head of state, Kim Yong-Nam, urged all military personnel to pledge their loyalty to Kim Jong-Un.
"Being loyal to Comrade Kim Jong-Un's leadership is the decisive guarantee to carry forward with the Great Comrade Kim Il-Sung and Kim Jong-Il's thoughts and accomplishments," he was quoted as saying by the ruling party newspaper, Rodong Sinmun.