(Opponents in bold indicate Glentoran played at home in the first leg)
European Cup/Champions League |
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| Season | Round | Opponents | Country | 1st Leg | 2nd Leg | Agg. | ||||
| 1964/65 | 1 | Panathinaikos | Greece | 2-2 | 2-3 | 4-5 | ||||
| 1967/68 | 1 | Benfica | Portugal | 1-1 | 0-0 | 1-1 | ||||
| 1968/69 | 1 | Anderlecht | Belguim | 0-3 | 2-2 | 2-5 | ||||
| 1970/71 | 1 | Waterford United | Republic of Ireland | 1-3 | 0-1 | 1-4 | ||||
| 1977/78 | 1 | Valur Rekjavik | Iceland | 0-1 | 2-0 | 2-1 | ||||
| 1977/78 | 2 | Juventus | Italy | 0-1 | 0-5 | 0-6 | ||||
| 1981/82 | 1 | Progrès Niederkorn | Luxembourg | 1-1 | 4-0 | 5-1 | ||||
| 1981/82 | 2 | CSKA Sofia | Bulgaria | 0-2 | 2-1 | 2-3 | ||||
| 1988/89 | 1 | Spartak Moscow | Russia | 0-2 | 1-1 | 1-3 | ||||
| 1992/93 | 1 | Olympique Marseille | France | 0-5 | 0-3 | 0-8 | ||||
| 1999/00 | Q1 | Litex Lovech | Bulgaria | 0-3 | 0-3 | 0-6 | ||||
| 2003/04 | Q1 | HJK Helsinki | Finland | 0-0 | 0-1 | 0-1 | ||||
| 2005/06 | Q1 | Shelbourne | Republic of Ireland | 1-2 | 1-4 | 2-6 | ||||
| 2009/10 | Q2 | Maccabi Haifa | Israel | 6-0 | 0-4 | 10-0 | ||||
Fairs/UEFA Cup
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| Season | Round | Opponents | Country | 1st Leg | 2nd Leg | Agg. | ||||
| 1962/63 | 1 | Real Zaragoza | Spain | 0-2 | 2-6 | 2-8 | ||||
| 1963/64 | 1 | Patrick Thistle | Scotland | 1-4 | 0-3 | 1-7 | ||||
| 1965/66 | 1 | Royal Antwerp | Belguim | 0-1 | 3-3 | 3-4 | ||||
| 1969/70 | 1 | Arsenal | England | 0-3 | 1-0 | 1-3 | ||||
| 1971/72 | 1 | Eintracht Braunschweig | West Germany | 0-1 | 1-6 | 1-7 | ||||
| 1975/76 | 1 | Ajax | Holland | 1-6 | 0-8 | 1-14 | ||||
| 1976/77 | 1 | FC Basel | Switzerland | 3-2 | 0-3 | 3-5 | ||||
| 1978/79 | 1 | IBV Vestmannaeyjar | Iceland | 0-0 | 1-1 | 1-1 | ||||
| 1982/83 | 1 | Banik Ostrava | Czechoslovakia | 1-3 | 0-1 | 1-4 | ||||
| 1984/85 | 1 | Standard Liège | Belguim | 1-1 | 0-2 | 1-3 | ||||
| 1989/90 | 1 | Dundee United | Scotland | 1-3 | 0-2 | 1-5 | ||||
| 2000/01 | Q1 | Lillestrøm SK | Norway | 0-3 | 0-1 | 0-4 | ||||
| 2001/02 | Q1 | FC Midtjylland | Denmark | 1-1 | 0-4 | 1-5 | ||||
| 2002/03 | Q1 | Wisla Kraków | Poland | 0-2 | 0-4 | 0-6 | ||||
| 2004/05 | Q1 | Allianssi Vantaa | Finland | 2-2 | 2-1 | 4-3 | ||||
| 2004/05 | Q2 | IF Elfsborg | Sweden | 0-1 | 1-2 | 1-3 | ||||
| 2006/07 | Q1 | SK Brann Bergen | Norway | 0-1 | 0-1 | 0-2 | ||||
| 2007/08 | Q1 | AIK Solna | Sweden | 0-5 | 0-4 | 0-9 | ||||
Cup-Winners' Cup
|
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| Season | Round | Opponents | Country | 1st Leg | 2nd Leg | Agg. | ||||
| 1966/67 | 1 | Glasgow Rangers | Scotland | 1-1 | 0-4 | 1-5 | ||||
| 1973/74 | 1 | Chimia Rimnicu Vilcea | Romania | 2-2 | 2-0 | 4-2 | ||||
| 1973/74 | 2 | SK Brann Bergen | Norway | 1-1 | 3-1 | 4-2 | ||||
| 1973/74 | QF | Borussia Mönchengladbach | West Germany | 0-2 | 0-5 | 0-7 | ||||
| 1983/84 | 1 | Paris Saint-Germain | France | 1-2 | 1-2 | 2-4 | ||||
| 1985/86 | 1 | Fram Reykjavik | Iceland | 1-3 | 1-0 | 2-3 | ||||
| 1986/87 | 1 | Lokomotiv Leipzig | East Germany | 1-1 | 0-2 | 1-3 | ||||
| 1987/88 | 1 | RoPS Rovaniemi | Finland | 0-0 | 1-1 | 1-1 | ||||
| 1990/91 | 1 | Steaua Bucuresti | Romania | 1-1 | 0-5 | 1-6 | ||||
| 1996/97 | Q | Sparta Praha | Czech Republic | 1-2 | 0-8 | 1-10 | ||||
| 1998/99 | Q | Maccabi Haifa | Israel | 0-1 | 1-2 | 1-3 | ||||