The lymph node ratio (LNR) has been proposed as an independent prognostic factor for survival in patients with oral squamous cell carcinoma (OSCC). However, little attention has been paid to its role in the specific subsite of the floor of the mouth (FOM). The purpose of this study was to evaluate the prognostic significance of the LNR in patients with FOM SCC. A retrospective analysis of 92 patients with FOM SCC who were treated with primary curative resection and neck dissection was conducted. Overall survival (OS) and disease-free survival (DFS) were used to evaluate the prognostic significance of the LNR. Both of these parameters were significantly worse (P < 0.001) in patients with neck metastases. The mean LNR was 0.145 in patients with positive lymph nodes. A LNR <0.145 was predictive of longer DFS, while the receiver operating characteristic curve analysis demonstrated that a LNR ≥0.175 indicated a significantly lower OS. This study confirms that metastatic cervical lymph nodes correlate with an adverse prognosis in patients with FOM SCC, and specifically, a LNR ≥0.145 is predictive. Therefore, the LNR in patients with FOM SCC may be a predictor of survival in these patients.