Copyright # 2020 by Mutaz B. Habal, MDPurpose: The aim of this study is to present reliable data by measuring the morphometric properties of the mandible in the fetal period. Methods: A study was performed on mandibles of 35 fetuses (18 male fetuses and 17 female fetuses), aged between 21 and 40 weeks of gestation. Fetuses were examined in 3 groups according to their developmental stages: 2nd trimester, 3rd trimester, and full-term. Morphometric measurements were performed for both the right and left sides of each mandible. The measurements of the mental foramen were performed using a digital caliper, and other measurements were performed using the ImageJ program. The data obtained were analyzed using the SPSS 20 for Windows program. Results: There was no significant gender difference for all parameters. When the parameters were compared by the trimesters, no significant difference was determined in the 2nd trimester - 3rd trimester, 3rd trimester-full-term, and second trimester - full-term comparisons of the angle of the mandible, and there was a significant difference in all other parameters (P < 0.05). According to the trimesters, all parameters, except the angle of the mandible, increased naturally with the development of the mandible. It was observed that the angle of the mandible decreased from the 2nd trimester to the 3rd trimester and increased from the 3rd trimester to the full term. When the right and left measurements were compared, no significant difference was found for all parameters in both general and trimester groups. Conclusion: The present study includes fetal mandibular parameters that have not been reported elsewhere. It is thought that the obtained data will contribute to the determination of anomalies, pathologies, and variations.