Background Musculus depressor septi nasi and its tendon, the dermocartilaginous ligament, play an important role in external nasal valve and nasal respiration. If the ligament is cut during septorhinoplasty operations, nasal functions of the nose and facial expressions are affected. Therefore, the aim of this study was to investigate the role of M. depressor septi nasi in nasal respiration at open rhinoplasty operations using rhinomanometry and electromyography. Methods The study included 29 patients who had only external nasal deformity (nasal hump deformity). All patients underwent open rhinoplasty. The dermocartilaginous ligament of the patients in the study group (DCL + group) was repaired but not in the control group (DCL - group). Rhinomanometry and electromyography were applied to all patients preoperatively and postoperatively. Results In the DCL - group, right and left nasal airflow values were significantly lower in post-op (562.92 cm(3)/s and 548.57 cm(3)/s), whereas right, left, and total nasal resistances were significantly lower in pre-op (0.28 Pa/cm(3)/s, 0.22 Pa/cm(3)/s, and 0.11 Pa/cm(3)/s). Statistically significant differences were not found between rhinomanometric measurements in pre-op and post-op values of the DCL + group. Post-op right, left and mean values of M. depressor septi nasi amplitude in the DCL + group (2.05 mV, 2.0 mV, 2.02 mV) were significantly higher than those in the DCL - group (1.52 mV, 1.61 mV, 1.57 mV). Conclusion Repair of the dermocartilaginous ligament during open rhinoplasty operations enhances nasal respiratory functions by expanding the external nasal valve through M. depressor septi nasi and allows the nose to participate in mimic movements.