Purpose <p>Acoustic analysis is an objective and quantitative method in diagnosing speech disorders and evaluating treatment efficacy. Although many reports have used acoustic analysis for oral cancer patients, few studies have focused on the extent of tongue resection. The aim of this study was to evaluate the usefulness of acoustic analysis in the assessment of postoperative speech impairment in oral cancer patients.</p> Methods <p>Postoperative speech data as well as Speech Handicap Index (SHI) and 5-point speech intelligibility scale were collected from 65 patients including 31 cases of oral cancer resection without glossectomy, 18 cases of partial glossectomy, and 16 cases of subtotal glossectomy. Speech data were acoustically analyzed by triangular vowel space area, vowel articulation index (VAI), first (F1) and second (F2) formant slopes, and compared according to the extent of tongue resection.</p> Results <p>The frequency of speech impairment assessed by SHI and 5-point speech intelligibility scale was differed according to the extent of tongue resection. As acoustic analysis, VAI and F1 slope in cases of subtotal glossectomy were significantly smaller than those in cases of partial glossectomy. F2 slope in cases of subtotal glossectomy was significantly smaller than those in the other cases.</p> Conclusion <p>Acoustic analysis was potentially useful as an objective speech assessment for the patients who underwent oral cancer surgery.</p>