The Ota Railway Co. opened the Mito - Kami-Sugaya - Hitachi-Ota line between 1897 and 1899, but was declared bankrupt in 1901. The 15 banks owed money formed the Mito Railway Co. to acquire the line and continue its operation. That company opened the Kami-Sugaya - Hitachi-Omiya section in 1918, resulting in the Kami-Sugaya - Hitachi-Ota line becoming the branch. The mainline was extended to Hitachi-Daigo in sections between 1922 and 1927, the year the company was nationalised. In 1929 JGR opened the Asaka-Nagamori - Yatagawa section, extending it to Kawahighashi in 1931. The Hitachi-Daigo - Iwaki-Tanakura section was opened in stages between 1930 and 1932, and the Kawahigashi - Iwaki-Tanakura section opened in 1934, completing the line. Freight services ceased between 1982 and 1987. CTC signalling was commissioned on the entire line in 1983.
Former connecting lines
Iwaki-Tanakura station - A 23 km line to Shirakawa was opened by the Shirotana Railway Co. in 1916. The line was nationalised in 1941, and closed in 1944. Plans to reopen the line in 1953 resulted in a decision to convert the line to a dedicated busway, which opened in 1957.
Hitachi-Ota station - An 11 km line to Omika was opened by the Johoku Electric Railway in 1928/29. In 1944 the company merged with the Hitachi Electric Railway, and a 7 km line to Akukawa was opened in 1947. Both lines were electrified at 600 VDC from opening. CTC signalling was commissioned in 1969, and in 1971 the lines became the first electric railway in Japan converted to one-person operation. Both lines closed in 2005.
There is generally one train every one to two hours, but between Mito and Kami-Sugaya this increases to one to two trains per hour. Only 13 trains per day run the entire length of the line; most services are from Mito to Hitachi-Ōmiya, to Hitachi-Daigo, and to Hitachi-Ōta. Between Hitachi-Daigo and Kōriyama there are few trains, with a period of 2–3 hours during midday having no services whatsoever. There are three additional trains between Hitachi-Daigo and Kōriyama, a single round-trip to Kōriyama from Iwaki-Ishikawa and back, and a single evening trip from Kōriyama to Iwaki-Tanakura that proceeds to Mito the following morning. Other seasonal trains are added on certain days throughout the year.
