Although orthodontic treatment improves dentoalveolar problems, the facial profile seldom changes because the perioral muscles do not easily adapt to the new morphological circumstances. We employed proprioceptive neuromuscular facilitation (PNF), which is training with added resisted movement to motions such as lifting the upper lip, lowering the lower lip, and sticking out the tongue, to adapt the perioral muscles to the new morphological circumstances. The subjects were 40 adults with an average age of 29.6 years. A series of PNF exercises was performed three times per day for 1 month. Lateral facial photographs were taken using a digital camera before training (T₀), after training (T₁), and 1 month after the end of training (T₂). The nasolabial (NL), mentolabial (ML), and mentocervical (MC) angles were measured, and linear measurements were taken to verify the change of each measurement point. In the test group, the NL and ML angles significantly increased (P < 0.05), and the MC angle significantly decreased after the PNF exercise. From T₁ to T₂, the NL and ML angles decreased significantly, while the MC angle increased significantly. No significant differences were observed in these angles when the values measured at T₀ and T₂ were compared. Although the training appeared to be effective for sharpening the mouth and submandibular region, continued training is necessary to avoid relapse. (J. Oral Sci. 50, 45-51, 2008)