| Country: | TUR |
| Type: | otoyol |
| Route: | 21A |
| Established: | 1992 |
| Direction A: | West |
| Terminus A: | near Tepeköy, Konya |
| Direction B: | East |
| Terminus B: | near Eminlik, Niğde |
| Length Km: | 32 |
| Regions: | Central Anatolia |
| Provinces: | Konya, Niğde |
| Map: | Karte O21 TR 2015.svg |
| Previous Type: | O |
| Previous Route: | 21 |
| Next Type: | O |
| Next Route: | 22 |
Otoyol 21A, abbreviated as O-21A, is a 32km (20miles) long auxiliary otoyol connecting the D.330 and D.750 to the O-21. The motorway was opened in 1992 as a connecting route to Konya and passes through mostly uninhabited rural land. The O-21A is a part of the E90.
The motorway was deemed too short to receive its own O-XX designation, despite being longer than the O-50, but too long to be designated as an exit; therefore, the route was signed as the O-21A, and is the only otoyol route in Turkey to have an alpha-numeric route designation.
| width=100 | Province ! | width=100 | District ! | width=40 | km ! | width=40 | mi ! | width=30 | Exit ! | width=300 | Destination ! | width=200 | Notes |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Konya | Ereğli | style='background: #dcdcdc' | 0.0 | style='background: #dcdcdc' | 0.0 | - | — Konya | Continues as the D.330 | |||||
| style='background: #dcdcdc' | 0.6 | style='background: #dcdcdc' | 0.4 | K153 | — Zonguldak, Tarsus | ||||||||
| Niğde | style='background: #dcdcdc' | 17.6 | style='background: #dcdcdc' | 10.9 | K152 | — Niğde, Ulukışla | |||||||
| style='background: #dcdcdc' | 28.8 | style='background: #dcdcdc' | 17.9 | K151 | Eminlik | ||||||||
| style='background: #dcdcdc' | 30.1 | style='background: #dcdcdc' | 18.7 | ||||||||||
| style='background: #dcdcdc' | 32.3 | style='background: #dcdcdc' | 20.1 | style='background: #ccccff' | K15 | style='background: #ccccff' | — Niğde, Tarsus | style='background: #ccccff' | |||||
