Line S9 is a north–south suburban metro line in the Nanjing Metro (Chinese: 南京地铁S9号线; pinyin: Nánjīng Dìtiě S-Jiǔ Hào Xiàn) system, which opened on December 30, 2017.^[4] It connects to Line S1 at Xiangyulunan and crosses Shijiu Lake on a 12 km (7.5 mi) long bridge between Mingjue and Tuanjiewei.^[5]

Line S9 also serves as the second stage of the Nanjing–Gaochun Intercity Railway, with Line S1 serving as the first stage. In June 2019 a few express trains started operating during rush hour, running non-stop between Xiangyulunan and Gaochun.^[6]

Line S9 uses car Class B aluminum alloy trains with a maximum service speed of 120 km/h (75 mph).^[7] The train cars are 2.8 meters (9 ft 2 in) wide with a transverse 2+2 seating layout, with 151 seats and a capacity of 441 people.^[8] Unlike most Class B metro trains, each car only has 3 doors per side instead of 4, owing to the line's length and speed.