| Prevseason: | 2007–08 |
| Nextseason: | 2009–10 |
| Season: | 2008–09 |
| Champions: | Union Olimpija 15th title |
| Runners Up: | Helios Domžale |
| Semifinalists: | Krka Zlatorog |
| Tv: | RTV Slovenija Šport TV |
| Teams: | 12 + 1 |
| Duration: | 30 September 2008 – 9 June 2009 |
| Top Seed: | Union Olimpija |
| Mvp: |  Shawn King |
| Ppg: | 22.2 |
| Rpg: | 14.8 |
| Apg: | 4.6 |
The 2008–09 Slovenian Basketball League (official: 2008–09 UPC League) was the 18th season of the Premier A Slovenian Basketball League, the highest professional basketball league in Slovenia. Union Olimpija won its 15th national championship.
| Team | City | Arena | Capacity | Head coach |
|---|---|---|---|---|
| Alpos Šentjur | Šentjur | Hruševec Sports Hall | 800 | Boštjan Kočar |
| CPG Nova Gorica | Nova Gorica | Sports Hall OŠ Milojke Štrukelj | 400 | Dejan Gašparin |
| Elektra Esotech | Šoštanj | Šoštanj Sport Hall | 600 | Borut Cerar |
| Epic Misel Postojna | Postojna | Sports Hall ŠC Postojna | 400 | Aleš Lenassi |
| Geoplin Slovan | Ljubljana | Kodeljevo Sports Hall | 1,540 | Miro Alilović |
| Helios Domžale | Domžale | Komunalni center Hall | 2,500 | Rade Mijanović |
| Hopsi Polzela | Polzela | Polzela Sport Hall | 1,800 | Boštjan Kuhar |
| Krka | Novo Mesto | Leon Štukelj Hall | 2,800 | Ivan Sunara |
| Luka Koper | Koper | Arena Bonifika | 4,000 | Ivan Stanišak |
| TCG Mercator | Škofja Loka | Sports Hall OŠ Poljane | 400 | Matic Vidic |
| Union Olimpija | Ljubljana | Tivoli Hall | 4,050 | Jure Zdovc |
| Zagorje | Zagorje | Sports Hall Zagorje ob Savi | 800 | Dušan Hauptman |
| Zlatorog Laško | Laško | Tri Lilije Hall | 2,500 | Aleš Pipan |
| Teams from the Adriatic League |
| Pos | Team | P | W | L | F | A | Pts | |
| 1 | Krka | 22 | 19 | 3 | 1841 | 1588 | 41 | |
| 2 | Helios Domžale | 22 | 18 | 4 | 1822 | 1511 | 40 | |
| 3 | Zlatorog Laško | 22 | 17 | 5 | 1761 | 1741 | 39 | |
| 4 | Geoplin Slovan | 22 | 15 | 7 | 1791 | 1720 | 37 | |
| 5 | Hopsi Polzela | 22 | 12 | 10 | 1787 | 1697 | 34 | |
| 6 | Elektra Esotech | 22 | 9 | 13 | 1633 | 1749 | 31 | |
| 7 | Luka Koper | 22 | 8 | 14 | 1747 | 1826 | 30 | |
| 8 | Zagorje | 22 | 8 | 14 | 1650 | 1807 | 30 | |
| 9 | TCG Mercator | 22 | 8 | 14 | 1561 | 1715 | 30 | |
| 10 | Alpos Šentjur | 22 | 7 | 15 | 1641 | 1734 | 29 | |
| 11 | Epic Misel Postojna | 22 | 7 | 15 | 1575 | 1825 | 29 | |
| 12 | CPG Nova Gorica | 22 | 4 | 18 | 1543 | 1759 | 26 |
P=Matches played, W=Matches won, L=Matches lost, F=Points for, A=Points against, Pts=Points
| Pos | Team | P | W | L | F | A | Pts |
| 1 | Union Olimpija | 14 | 13 | 1 | 1126 | 898 | 27 |
| 2 | Helios Domžale | 14 | 12 | 2 | 1172 | 1029 | 26 |
| 3 | Krka | 14 | 9 | 5 | 1067 | 1039 | 23 |
| 4 | Zlatorog Laško | 14 | 7 | 7 | 1098 | 1054 | 21 |
| 5 | Geoplin Slovan | 14 | 6 | 8 | 1066 | 1142 | 20 |
| 6 | Hopsi Polzela | 14 | 5 | 9 | 1074 | 1154 | 19 |
| 7 | Luka Koper | 14 | 2 | 12 | 1119 | 1296 | 16 |
| 8 | Elektra Esotech | 14 | 2 | 12 | 1065 | 1175 | 16 |
| Qualified for the Playoff stage |
| Pos | Team | P | W | L | F | A | Pts |
| 1 | TCG Mercator | 30 | 12 | 18 | 2155 | 2302 | 42 |
| 2 | Zagorje | 30 | 12 | 18 | 2275 | 2440 | 42 |
| 3 | Alpos Šentjur | 30 | 11 | 19 | 2256 | 2339 | 41 |
| 4 | Epic Misel Postojna | 30 | 10 | 20 | 2133 | 2417 | 40 |
| 5 | CPG Nova Gorica | 30 | 9 | 21 | 2146 | 2336 | 39 |
| bgcolor=F6CECE | Qualified for Relegation Playoffs | |
| bgcolor=F5A9A9 | Relegated to Second Division | |
| Pos | Team | P | W | L | F | A | Pts |
| 1 | Rudar Trbovlje | 4 | 3 | 1 | 370 | 329 | 7 |
| 2 | Epic Misel Postojna | 4 | 2 | 2 | 322 | 328 | 6 |
| 3 | Rogaška | 4 | 1 | 3 | 301 | 334 | 5 |
| width=50% valign=top | Performance Index Rating |
| width=50% valign=top |
|}|}
| width=50% valign=top | Rebounds |
|}|}