The Nankai Main Line is one of the two main railway lines of Japanese private railway company Nankai Electric Railway, together with Kōya Line. The route is from Namba Station in south downtown of Osaka to Wakayamashi Station in Wakayama via Sakai, Izumiōtsu, Kishiwada, Kaizuka, Izumisano, Sennan, Hannan and Misaki municipalities. The proper name is with the company's name, "the Nankai Main Line", not simply "the Main Line" often seen in other Japanese private railways. Lines of the Nankai Main Lane and the connecting lines excluded the Kōya Line and the Airport Line are named generically "the Nankai Line ". The line is shown with a pictogram of waves, or distinguished with blue from conifer or green Kōya Line.

Nankai Electric Railway Co., Ltd. is a private railway in Japan, founded in 1884. The name Nankai comes from the company's routes along the Nankaidō, the old highway that ran south from the old capital, Kyoto, along the sea coast. Nankai predates all the electric railways in the Tokyo region.