Nakatsu (中津市, Nakatsu-shi) is a city located on the northern border of Ōita Prefecture in Kyushu, Japan. The city is situated on the border with Fukuoka Prefecture.

The city was founded on April 20, 1929. As of 2008, the city has an estimated population of 84,179, with a population density of 171 people per km². The total area is 491.09 km².

• 1587: Kuroda Yoshitaka (Josui) built Nakatsu Castle as a flatland castle near the Yamaguni-River.
• April 1925: The village of Ōe is merged with Toyoda to become the town of Nakatsu.
• April 1919: The village of Ogusu and the town of Nakatsu join to become the city of Nakatsu.
• August 1933: The villages of Tsurui, Ōhata and Josui merge with the growing city of Nakatsu.
• April 1951: The village of Miho joins Nakatsu.
• October 1954: The village of Wada also joins.
• February 1955: The village of Imazu becomes part of Nakatsu.
• March, 2005: The village of Sankō and the towns of Honyabakei, Yabakei and Yamakuni all merge with Nakatsu.

Nakatsu is located in the northwest corner of Ōita Prefecture, Kyushu. To the east of Nakatsu is Usa, and to the southwest is Hita. Nakatsu touches the border of Fukuoka Prefecture on its west. To the northeast is the Suohnada Sea. The city covers an area of 491.09 square kilometers, 80% of which is mountainous. There is a wide stretch of flat, agricultural land which begins at the mouth of Yamakuni River and extends to Mt. Hiko.