Leinster proved too strong for their Irish rivals in the Magners League play-off semi-final in Dublin.
Fergus McFadden's try and two Jonathan Sexton penalties gave the hosts a deserved 11-0 lead at the break.
Ruan Pienaar gave Ulster hope with a superb long-range penalty, but Luke Fitzgerald's late try sealed Leinster's place in the grand final.
However, Brian O'Driscoll was among the Leinster players injured ahead of the Heineken Cup final with Northampton.
Leinster enjoyed a stiff breeze at their backs in the first half at a sunkissed RDS.
The hosts surged forward from the start, and Sexton fired over the first points after three minutes.
Fitzgerald missed out on a try after knocking on from a pass while Sexton kicked wide with a long-range penalty attempt.
Ulster were guilty of unforced errors, and this led to McFadden's try on 21 minutes, with the winger going in at the corner from an Isa Nacewa pass.
Sexton's conversion attempt hit a post before injuries forced Leinster to make two changes, with Eoin Reddan and Stan Wright replacing Issac Boss and Mike Ross.
Leinster edged further ahead when Sexton slotted over a penalty with the last kick of the half.
O'Driscoll, who suffered a knee injury in the first half, was replaced at the break by David Kearney.
Ulster enjoyed their first spell of pressure on the restart but they failed to make it count after Ian Humphreys sent his penalty narrowly wide.
Another Ulster attack ended with the visitors conceding a penalty close to the Leinster line.
Richardt Strauss hobbled off to join Boss, Ross and O'Driscoll as Leinster injury concerns for next weekend's Heineken Cup decider against Northampton.
Ulster finally got on the scoreboard on 61 minutes thanks to Pienaar's audacious penalty from his own half.
Fitzgerald ended Ulster hopes of a comeback when he burst through and touched down under the posts for a fine individual try with eight minutes left.
McFadden increased the gap to 15 points with the simple conversion as Leinster eased through to the grand final against Munster or the Ospreys in a fortnight.
Leinster: I Nacewa; F McFadden, B O'Driscoll, G D'Arcy, L Fitzgerald, J Sexton, I Boss; C Healy, R Strauss, M Ross, L Cullen (cpt), N Hines, S O'Brien, S Jennings, J Heaslip.
Replacements: J Harris-Wright, H van der Merwe, S Wright, D Toner, K McLaughlin, E Reddan, I Madigan, D Kearney.
Ulster: A D'Arcy, C Gilroy, D Cave, N Spence, S Danielli, I Humphreys, R Pienaar; T Court, R Best (cpt), D Fitzpatrick, J Muller, T Barker, P Wannenburg, C Henry, R Diack.
Replacements: A Kyriacou, P McAllister, J Cronin, N McComb, T Anderson, P Marshall, I Whitten, C Gaston.