The decision came following China's National People's Congress standing committee's earlier designation of Sept 3 as the "Victory Day of the Chinese people's war of resistance against Japanese aggression," and of Dec 13 as "Nanjing Massacre Memorial Day."
A ceremony will be held Sept 3, at which the chief executive, senior government officials, judicial officers, legislators, representatives of war veteran groups and members of the community will attend, according to an office statement.
Another memorial ceremony will be held Dec 13, but details are pending, it said.
Following the end of the 44-month Japanese occupation of Hong Kong in 1945, the then British colony had designated Aug. 30 as Liberation Day to commemorate Britain's resumed governance of the territory.
The memorial was cancelled shortly following Hong Kong's return to Chinese rule in 1997.