Line 4 is a loop line of the Shanghai Metro network. Its older rolling stock carry a bright purple colour belt to differentiate them from Line 3 trains which share a portion of its route, while the newer stock features a yellow and purple livery, which the exact line is labelled using sticker or screens saying “Line 3” or “Line 4”. To determine the direction of travel, the line that travels counter-clockwise is called the Outer Loop (外环), while the other line is known as the Inner Loop (内环). Although it is a loop line, trains returning to the depot use Yishan Road as a terminal to let all passengers disembark. The first segment of the line between Damuqiao Road and Lancun Road opened on December 31, 2005. The remainder of the line opened on December 29, 2007. The line is colored purple on system maps.

The Shanghai Metro (Chinese: 上海地铁; pinyin: Shànghǎi Dìtiě; Shanghainese: Zaon6he5 Di6thiq7) is a rapid transit system in Shanghai, operating urban and suburban transit services to 14 of its 16 municipal districts and to the neighboring township of Huaqiao, in Kunshan, Jiangsu Province.