PURPOSE: To investigate the myofunctional characteristics of nasal and oral breathing in obese individuals. METHODS: Participants were 24 obese individuals with ages between 8 and 15 years, who participated in the Obesity Group of the Ambulatory of Pediatrics of an University Hospital, and were selected by convenience. The myofunctional characteristics were assessed using the Orofacial Myofunctional Assessment with Scales (Avaliação Miofuncional Orofacial com Escalas - AMIOFE) protocol. RESULTS: Oral breathing was present in 62.5%, and nasal breathing in 37.5% of the population studied. In the oral breathing group, 40% of the subjects presented lips tension during occlusion and 80% showed a narrow palate, while almost all nasal breathers had normal palate and lips posture (p<0.05). Interposition of the tongue in the dental arches occurred in 47% of oral breathers and none of the nasal breathers. Oral breathers showed the tendency not to repeat the swallowing of the same bolus. No difference was found between groups regarding face appearance, jaw posture, cheeks, and chewing function. CONCLUSION: Oral breathing in obese children and adolescents was accompanied by myofunctional alterations of the stomatognathic system, represented by narrow palate, interposition of the tongue in the dental arches, occlusion of the lips with tension, and swallowing disorders.