Objectives <p>The aim of this study was performed to investigate the apparent diffusion coefficient (ADC) for distinguishing between benign and malignant lesions in submandibular and sublingual spaces.</p> Methods <p>Thirteen patients with benign and malignant lesions in submandibular and sublingual spaces were evaluated by MRI. The MRI were obtained by a 1.5&#xa0;T MR unit using a head coil, and included T1-weighted image (T1WI), T2-weighted image (T2WI) and diffusion-weighted image (DWI). The ADC maps were calculated automatically by the DWI obtained with b = 800&#xa0;s/mm². We placed regions of interest (ROI) to measure the ADC values on ADC maps, and the ADC value were automatically analyzed. The ADC in benign and malignant lesions were compared by Mann–Whitney U test with a 5% significance level.</p> Results <p>Regarding all lesions, T1WI, T2WI and DWI showed low-, high- and high-signal intensity area, respectively. The ADC of malignant lesions (1.10 ± 0.05 × 10^–3 mm²s⁻¹) was lower than those of benign lesions (2.36 ± 0.64 × 10^–3 mm²s⁻¹, p = 0.001).</p> Conclusion <p>The ADC could be effective for the objectively and quantitatively diagnosis of submandibular and sublingual malignant tumors.</p>