The surgical management of retromolar trigone cancer (RTC) is an area of contention regarding the extent of bony resection. We aim to evaluate the oncological safety and feasibility of posterior marginal mandibulectomy (PMM) for RTC. We analyzed the clinical records of 98 patients with squamous cell carcinoma managed surgically using marginal mandibulectomy during 2014 to 2017, in which anterior segment mandibulectomy (AMM) and PMM were done in 56 and 42 patients, respectively. The median follow-up time was 44.4 months (95% confidence interval [CI] 42.3, 49.5) and the overall survival rate was 93.9% (95% CI 89.4–98.8%). The local recurrence rate was 19.6 and 18.3 % in PMM and AMM (p = 0.854). In the PMM group, osteoradionecrosis (ORN) was detected in two patients (4.3%) and fractures in one (2.1%) patient, while the AMM group neither had fracture nor ORN till the latest follow-up. The study results suggest that PMM is an oncological safe and adequate procedure for RTC.