OBJECTIVES: The purpose of this study was to compare the effects of a differently designed functional appliance (R-appliance) and the Anterior Inclined Bite Plate (AIBP) in Class II Division I (Cl II Div I) cases. MATERIAL AND METHODS: Fifty patients (28 girls, 22 boys) were chosen for the study: 25 patients (13 girls, 12 boys) with mean age of 10.4±0.8 years were treated with R-appliance for 11±2 months, the other 25 patients (15 girls, 10 boys) with mean age of 9±1.2 years were treated with AIBP for 10±2 months. All patients had Cl II Div I malocclusion due to mandibular deficiency. Lateral cephalograms were analyzed at the beginning (T1, T 1) and end of the study (T2, T 2). RESULTS: Paired T-test showed that SNB had a significant increase in both groups. The same test revealed that IMPA was reduced in R-appliance for 3.1±4.7 (p<0.01), but it was increased for 0.1±5.1 (p<0.9) in AIBP group. T-test showed that the inter-group difference of IMPA was statistically significant (p<0.05). SNA showed an increase in both groups (p<0.9). Ar-B and Ar-Pog showed an increase in both groups and the differences between them were statistically significant. CONCLUSIONS: Mandibular advancement was achieved in both groups, but R-appliance achieved this result without lingual tipping of lower incisors.