Nankai Electric Railway Co., Ltd. (南海電気鉄道株式会社, Nankai denki tetsudō kabushiki gaisha) is a private railway in Japan, founded in 1884. The name Nankai (which means "South Sea") 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.

The Nankai network branches out in a generally southern direction from Namba Station in Osaka. The Nankai Main Line connects Osaka to Wakayama, with an important spur branching to Kansai International Airport. The rapi:t α express connects Kansai International Airport to Namba in 34 minutes, while the rapi:t β takes 39 minutes with two additional stops. The Koya Line connects Osaka to Mt. Koya, headquarters of the Buddhist Shingon sect and a popular pilgrimage site. IC cards (PiTaPa and ICOCA) are accepted.

The Nankai Railway Company was founded on June 16, 1884. In 1944 it was one of the companies that merged to form Kinki Nippon Railway Co., Ltd. (Kin-nichi, present Kintetsu Railway). However, Kin-nichi transferred the former Nankai Railway Company's lines to the present Nankai Electric Railway Co., Ltd. (named Koyasan Electric Railway Co., Ltd. from March 28, 1925 until March 14, 1947) on June 1, 1947.

From 1938 to 1988, Nankai Electric Railway owned the Nankai Hawks, a team in Nippon Professional Baseball that was based in Osaka. The team was sold to Daiei after the 1988 season and moved to Fukuoka and rechristened the Fukuoka Daiei Hawks. The team was sold again in 2005 to SoftBank, and are now the Fukuoka SoftBank Hawks.

On November 1, 2024, Ministry of Land, Infrastructure, Transport and Tourism (MLIT) approved the merger of Nankai Electric Railway and its subsidiary Semboku Rapid Railway, effective April 1, 2025.

The following vehicles once made up the fleet of the Semboku Rapid Railway. They were transferred to Nankai on 1 April 2025.