Oral mucositis (MO) is considered to be the most severe stomatologic complication associated with antineoplastic treatment, which may lead to its interruption. Several current clinical protocols have aproven the benefits of Laser Photobiomodulation (LP) in the prevention and control of MO, due to its analgesic and anti-inflammatory effects and its stimulation of mesenchymal cells proliferation. The objective of this study was to evaluate the action of laser in initial events of chemo-induced MO. Eight Hamsters were divided into 2 groups (G): GI positive control (induction of MO) and GII Laser (induction of MO + Laser therapy). MO was induced by two injections of 5-Fluorouracil followed by grooves in the mucosa of the cheek pouch. The PL (Diode Laser of Gallium and Aluminum Arsenide, λ660nm, 40mW, 2,4J/cm2 ) was performed on day 0 of the experiment and every 48 hours until day 6. On day 7 the mucosa was photographed for clinical analysis according to Lima et al., 2005 and the animals were killed, for bag removal and histological processing for Hematoxylin and Eosin (H / E) staining. After statistical analysis (Fischer's Exact) with a significance level 0.5%, it was concluded that the LP, according to the adopted protocol, was able to prevent MO, and most hamsters showed no visible clinical changes in the cheek pouch. Histologically, it was observed that LP reduced angiogenesis and recruitment of inflammatory cells in G2. According to the results obtained LP was effective in preventing and reducing the severity of oral mucositis.