This study was designed to measure the tongue volume by a simplified method, and to evaluate the effects of tongue volume on both maxillary and mandibular dental arch lengths and widths. Forty children with a mean ages12 years old were selected for this study. The mouth breather group were consisted of 20 mouth breathing children, and the other 20 for the nasal breathing as a control group . The mouth breathers have an important character that the tongue is always restricted to the lower dental arch leaving the upper dental arch intact. So a comparative study was done to evaluate the effects of tongue volume on both arches in nasal breathing group (normal control group) and in mouth breathing group. It was found that the mean tongue volume in the mouth breathing group was 510.6 .with S.D +9.6 while for nasal breathing group was 523.4 with S.D + 10.3. Moderate to low or even negative correlations were found between the mouth breather tongue volumes and dental arch measurements especially in posterior region. Surprisingly there were no correlations recorded between tongue volume and dental arch measurements in nasal breathing group. So on the bases of the results obtained from this study it was found that there was variations of the effect of tongue volume on dental arch configuration in mouth breathing group if compared to the nasal breather group. Tongue impression method for dental casts could be considered as a reliable method for recording tongue volume.