12 April 1971: Beginning of construction of Line 1
15 August 1974: Line 1 Seoul Railway Station - Cheongnyangni (9.54km) & Metropolitan Subway Gyeongin Line (Guro-Incheon), Gyeongsu (Seoul Station-Suwon), Cheongnyangni-Seongbuk Line
9 March 1978: Beginning of construction of Line 2
9 Dec. 1978: Metropolitan Subway Gyeongwon Line (Yongsan-Hyukong)
29 Feb. 1980: Beginning of construction of Lines 3 & 4
31 Oct. 1980: Line 2 Sinseol-dong - Sports Complex (14.3km)
23 Dec. 1982: Line 2 Sports Complex - Seoul National Univ. of Education (5.5km)
16 Sept. 1983 Line 2 Seongsu-Euljiro (8km)
17 Dec. 1983: Line 2 Seoul National Univ. of Education - Seoul National University (6.7km)
22 May 1984 Line 2 City Hall - Seoul National University (19.2km)
20 April 1985: Line 4 Sanggye - Hansung University (11.8km)
12 July 1985: Line 3 Gupabal-Dongnimmun (8km)
18 Oct. 1985: Line 3 Dongnimmun - Yangjae (16.2km), Line 4 Hansung University - Sadang (16.4km)
2 Sept. 1986: Seongbuk-Uijeongbu Line (now operated with Line 1)
27 June 1990: Beginning of the construction of Line 5
13 July 1990: Line 3 Gupabal - Jichuk (1.5km)
22 May 1992: Line 2 Sindorim - Yangcheon-gu Office (2.7km)
21 April 1993: Line 4 Sanggye-Danggogae (1.2km)
30 Oct. 1993: Line 3 Yangjae-Suseo (7.5km)
1 April 1994: Line 4 Sadang - Namtaeryeong (2.2km) & Urban Subway Gwacheon Line (Geumjeong-Namtaeryeong, 14.1km)
1 Sept. 1994: Urban Subway Bundang Line (Suseo-Ori 18.5km)
15 Nov.1995: Line 5 Gangdong Wangsimni-Sangil-dong (14.5km)
30 Jan. 1996: Urban Subway llsan Line (Jichuk-Daehwa, 19.2km, now operated with Line 3)
29 Feb. 1996: Line 2 Sinjeong branch line Yangcheon-gu Office-Sinjeong 4way Street (1.9km)
20 March 1996: Line 2 Sinjeong branch line Sinjeong 4way street - Kkachisan (1.4km) & Line 5 Gangseo branch line Banghwa - Kkachisan (8.8km)
30 March 1996: Line 5 Geoyeo zone Gangdong - Macheon (18.5km)
12 Aug. 1996: Line 5 Youngdungpo zone Kkachisan-Yeouido (7.8km)
11 Oct. 1996: Line 7 Gagnbuk zone Jangam - Konkuk University (19km)
23 Nov. 1996: Line 8 Jamsil - Moran (13.1km)
30 Dec. 1996: Line 5 Yeouido - Wangsimni (14.1km)
3 Dec. 1996 - 22 Nov. 1999: Reconstruction of the Line 2 Dangsan Railway Bridge
2 July 1999: Line 8 Amsa - Jamsil (4.6km)
29 Feb. 2000: Line 7 Onsu - Sinpung (9.2km)
1 Aug. 2000: Line 7 Konkuk University - Sinpung (17km)
7 Aug. 2000: Line 6 Bonghwasan - Sangwolgok (4 km)
15 Dec. 2000: Line 6 Sangwolgok - Yeonsinnae (27km) except stations between Itaewon and Yaksu
9 March 2001: Line 6 remaining stations opened (Itaewon - Yaksu)
3 Sept. 2003: K2 Bundang Line Suseo - Seonneung (6.6km)