The study aimed to analyze morphometric assessment of the mesorectal fat thickness and its correlation with body mass index in Chinese Han population. The anterior, posterior, right lateral, and left lateral mesorectal fat thickness were measured using MRI T2-weighted images. The mean distance from the rectal wall to the mesorectal fascia were 3.8, 8.4, 11.3, and 11.7 mm in anterior, posterior, right lateral, and left lateral portion, respectively. The mesorectal area, rectal area, mesorectal fat thickness area, and rectal height were 2395.3 ± 691.1 mm², 709.6 ± 403.5 mm², 1685.7 ± 525.3 mm², and 9.1 ± 0.8 cm. BMI was found to be directly proportional to and statistically significant to the mesorectal fat area (p = 0.01). Since the mean mesorectal fat thickness was found to be <12 mm, T3d staged rectal cancer is less likely to be found in an average Chinese population that may affect the overall-survival and progression-free survival in rectal cancer patients. Anterior portion of the rectum was least thick compared to all other sides. Therefore, extra-caution should be taken in handling tumors on the anterior part of the rectum.