Marine Day (海の日, Umi no Hi^?), known as 'Ocean Day' or 'Sea Day' is a Japanese national holiday celebrated on the third Monday in July. Many people take advantage of the holiday and summer weather to take a beach trip.

The day was known as Marine Memorial Day (海の記念日 umi no kinen bi) until 1996. Communications Minister Shozo Murata designated the holiday in 1942 to commemorate the Meiji Emperor and his 1876 voyage in the Meiji-Maru, an iron steamship constructed in England in 1874. The voyage included a trip around the Ou district, embarking on a lighthouse boat in Aomori, and a brief stop in Hakodate before returning to Yokohama on July 20 of that year. "Marine Day" was declared a national holiday in 1995 as a day of gratitude for the blessings of the oceans and to hope for the economic prosperity of maritime Japan.