Introduction and Aim: An accurate determination of gestational age (GA) is crucial to the management of all pregnancies, particularly high-risk pregnancies. This study aimed to comparing between the accuracy of ultrasonographic fetal kidney length and Transcerebellar diameter in GA determination in third trimester. Patients and methods: The study was a cross sectional one, carried out at the department of Obstetrics and Gynecology, Damietta Faculty of Medicine, Al-Azhar University, Damietta, Egypt. The study had been performed between January 2021 and January 2022. All were submitted to a detailed history, routine antenatal investigations, general and obstetrical examination. Then, measurements of all fetal biometric parameters were recorded using a real- time, grayscale, 3.5–5.0 MHz curvilinear array transducer. Results were compared to the gestational age determined by last menstrual period. Results: The patient age ranged between 18 and 37 years, their weight ranged between 55 and 109 kg, while gravidity ranged between 1 and 5 and parity ranged between 0 and 4. The GA as determined by last menstrual period (LMP) was ranged between 28 and 40 weeks. The calculated GA by different measurements were also included and they were around the same measurements as determined by LMP.  This was confirmed by the absent statistically significant difference between GA by LMP and any of calculated gestational age by any method. The mean fetal kidney length is more accurate in determination of gestational age than transcerebellar diameter (96.3% vs 89.8%) and both were significantly correlated with other calculated gestational ages. Conclusion: The length of the fetal kidney length proportionately correlated with fetal gestation age with powerful correlation coefficient. Fetal kidney length is found to be more accurate in GA determination than transcerebellar diameter (TCD).