The mechanisms of action of photobiomodulation (PBM) in oral mucositis (OM) are not completely elucidated. To enlighten the role of PBM in the evolution of epithelial maturity in OM ulcers, the present study evaluated the effect of PBM with red ( ) wavelength of 660 nanometers (nm) and infrared of 780 nm in radio-induced OM wounds on the tongue of rats, eight and twenty days after irradiation with single dose of 20 Gy. The percentage area corresponding to positive staining for cytokeratin 10 (CK10) and 14 (CK14) proteins was evaluated in the epithelial area of the lesions, using an immunohistochemical technique (IHC), 8 and 20 days after the induction of lesions, and compared with an untreated control group. CK10 was significantly more expressed in the group treated with 660 nm PBM. CK14 did not show quantitative differences between the groups evaluated. However, whereas in the groups treated with PBM, CK14 was already restricted to the basal layer of the epithelium, as expected in healthy epithelia, in control group it was also expressed in upper layers of the epithelium. In this work, PBM was able to improve epithelial maturity of the repaired OM wound, especially in the 660 nm group.Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)Coordena????o de Aperfei??oamento de Pessoal de N??vel Superior (CAPES)Conselho Nacional de Desenvolvimento Cient??fico e Tecnol??gico (CNPq)FAPESP: 17/50332-0; 13/26113-6; 21/00633-0CAPES: 001CNPq: INTC-465763/2014-6; Sisfoton 440228/2021-2; PQ-314517/2021-9