The first section opened, between Tadotsu and Kotohira, was constructed by the Sanuki Railway Co. in 1889. The company was nationalised in 1906. The Kotohira - Awa Ikeda section was opened in 1914 and connected to the Tokushima line. The Susaki - Kochi - Kusaka section opened in 1924, and was extended north in sections 1925-35, where it connected to the northern section at Minawa, the line from Awa Ikeda having been extended there in 1931. The Susaki - Tosakume section opened 1939, with extensions to Kageno opening 1947 and to Kubakawa in 1951. CTC signalling was commissioned between Tadotsu - Kochi in 1967, and the 4,180m Oboke tunnel and associated realignment opened the following year. The 2,583m Osugi tunnel and associated realignment opened in 1973. CTC signalling was extended to Kubokawa in 1986, and the Tadotsu - Kotohira section was electrified the following year. Freight trains ceased operating between Tadotsu - Kochi in 2005.
Former connecting lines
Kotohira station - The Kotohira Express Railway Co. operated a 16 km line to Sakaide on the Yosan Line 1930-44, with the line formally closing in 1954.
Tadotsu station - The Kotohira Sangu Railway Co. operated a 27 km line to Sakaide 1922/28 - 1963, with a 7 km branch to Kotohira operated 1923-63.
Services
Nanpūlimited express trains make 14 round-trips per day between Okayama and Kōchi, Nakamura, or Sukumo. Shimanto limited expresses make five round trips per day between Takamatsu and Kōchi, Nakamura, or Sukumo. The Sunport'' rapid service trains link Kotohira and Takamatsu once an hour. The line is generally divided into three parts for local services at Awa-Ikeda and Kōchi. For the segment between Tadotsu and Kotohira, there are through services to/from Okayama and Takamatsu. The Tosa Kuroshio Railway Gomen-Nahari Line has through service to/from Kōchi.
Stations
Local trains generally stop at all stations, but sometimes skip stations marked "▽".
Sunport rapid trains stop at all stations on the Dosan Line.
See the articles on the Nanpū and Shimanto limited express services for details of station stops.
Trains are able to pass each other at stations marked "◇" and "◆" ; trains cannot pass at stations marked "|".