The 1991 Australian Under-21 Individual Speedway Championship was the 5th running of the Australian Under-21 Individual Speedway Championship organised by Motorcycling Australia. The final took place on 6 January 1991 at the Olympic Park Speedway in Mildura, Victoria. The championship was won by Mildura's own Leigh Adams who won the third of his four national Under-21 championships. Shane Parker from Adelaide was second with another Mildura rider Jason Lyons in third place. Parker defeated Lyons in a run-off for the minor placings after both finished the meeting on 13 points. Former South Australian champion Scott Norman defeated Dave Hamnett from New South Wales in a run-off for fourth place after both finished the meeting on 11 points.
| width=25px | Pos. | Rider | width=40px | Points | width=70px | Details |
|---|---|---|---|---|---|---|
| Leigh Adams | 15 | |||||
| Shane Parker | 13+3 | |||||
| Jason Lyons | 13+2 | |||||
| 4 | Scott Norman | 11+3 | ||||
| 5 | Dave Hamnett | 11+2 | ||||
| 6 | Mark Lemon | 10 | ||||
| 7 | Damon Richardson | 8 | ||||
| 8 | Jason Hawkes | 7 | ||||
| 9 | Cory Alderton | 7 | ||||
| 10 | Matthew Poole | 6 | ||||
| 11 | Brett Tomkins | 6 | ||||
| 12 | John Reid | 6 | ||||
| 13 | Clinton Butler | 4 | ||||
| 14 | Jamie Plumb | 2 | ||||
| 15 | Ty Platt | 1 | ||||
| 16 | Steven Butler | 0 | ||||
| 17 | Reece Davison (Res) | – | did not ride | |||
| 18 | Steve Graetz (Res) | – | did not ride |