Introduction. This study was performed prospectively and randomly to compare clinical outcomes of modified-Brostrom procedure using single and double suture anchor for chronic lateral ankle instability. Material & Methods. Forty patients were followed up for more than 2 years after modified-Brostrom procedure for chronic lateral ankle instability. Twenty modified-Brostrom procedures with single suture anchor and 20 procedures with double suture anchor randomly assigned were performed by one surgeon. The mean age was 30.6 years, and the mean follow-up period was 2.6 years. The clinical evaluation was performed according to the Karlsson scale and Sefton grading system. The measurement of talar tilt angle and anterior talar translation was performed through anterior and varus stress radiographs. Results. At the last follow-up, the Karlsson scale had improved significantly from preoperative average 45.4 points to 90.5 points in single suture anchor group, from 46.2 points to 91.3 points in double suture anchor group. There were 8 excellent, 10 good, and 2 fair results according to the Sefton grading system in single anchor group, and 9 excellent, 8 good, 3 fair results in double anchor group. Therefore, 18 cases (90%) in single anchor group and 17 cases (85%) in double anchor group achieved satisfactory results. Talar tilt angle had improved significantly from preoperative average 15.7° to 6.1° in single anchor group, from 16.8° to 4.2° in double anchor group. There was significant difference in postoperative talar tilt angle between single and double anchor group. Conclusion. Significant differences in clinical and functional outcomes were not found between single and double suture anchor technique. On stress radiographs for evaluation of mechanical stability, modified-Brostrom procedure using double anchor showed less talar tilt angle than single anchor technique