In this work, the effect of swirl on regression rate (rb) in a hybrid rocket motor is investigated numerically. The rb increased monotonically with inlet swirl number and was also found to depend on the inlet swirl profile. The swirl velocity profiles with the peak closer to the axis yielded higher rb. Parametric study on fuel grains of various lengths and diameters (L/D≤25) shows that swirl is more effective in improving the average rb for short grains (L/D<5) and large diameter grains. © 2013 Elsevier Masson SAS. All rights reserved.