Akaiwa (赤磐市, Akaiwa-shi) is a city located in Okayama Prefecture, Japan.
As of May 1, 2015, the city has an estimated population of 43,021, with 17,192 households and a population density of 205 persons per km². The total area is 209.43 km².
The modern city of Akaiwa was established on March 7, 2005, from the merger of the towns of Akasaka, Kumayama, San'yō and Yoshii (all from Akaiwa District).
Akaiwa is one of three remaining places in Japan that produces the bamboo stalk for fude ink brushes. The harvested bamboo stalks are spread in the dry riverbed of the Yoshii River during the winter to dry under the sun. The stalks are then boiled in the town to remove impurities.
Akaiwa is home to the Kumayama Archeological Site. The site was utilized as a sacred spot as early as the Yayoi period. A Buddhist temple, Reizan-ji, was active on Mount Kuma (507.8 m (1,666 ft)) from the early Nara to the Muromachi period. A 11.7 m (38 ft) stone base remains on the site, and is protected by the Japanese government. The stone base originally supported a large Buddhist statue.