National Day, also known as national day and national day anniversary, refers to a legal holiday formulated by a country to commemorate the country itself. It is usually the independence of the country, the signing of the constitution, or other significant anniversaries. On this day, every country will hold various celebrations. In ancient China, the emperor's accession to the throne and birthday were called "National Day".

The longest National Day in the history of the world is San Marino's national day. As far back as ad 301, San Marino designated September 3 as its own national day.

The national day of new China refers specifically to the anniversary of the official establishment of the people's Republic of China, so people all over the country will hold celebrations on October 1 every year. October 1st, 2019 is the 70th anniversary of the founding of the people's Republic of China.