Abstract : This study aimed to evaluate the effect of Intermaxillary lip bumper in the treatment of Class II/1-malocclusion compared with the Activator. This was a randomized, parallel, two arm, and single center trial. It consist of 40 (21 female and 19 male) patients with class II/1-malocclusion. They were divided equally into activator groups (11 male and 9 female) and Intermaxillary lip bumper group (10 male and 10 female). Pre-and post- treatment dental cast model were evaluated by measuring the intermolars widths, arch length, Overjet, overbite and arch depth. Wilcoxon signed-ranks tests were used for intra-group comparisons, whereas Mann-Whitney U tests were used for inter-group comparisons. The differences between the two groups were substantially different at 0.01 after Bonferroni correction. The differences in variables Overjet and Overbite were only significant in pre-and post-treatment intergroup (p≤0.01), whereas there is no significant differences between the studied groups (p≥0.01).