The treatment of diabetes mellitus (DM) is complex and involves different approaches. Photobiomodulation (PBM) has positive effects on biological tissues and therapeutic effects on different disorders. However, very little is known about the use of PBM for the treatment of DM per se and what would be the most appropriate dose. In this context, our aim was to evaluate the effects of PBM used in 2 different doses in diabetic rats. Twenty-four Wistar rats were used in this study and distributed into 3 groups: diabetic control group (CG), diabetic group that underwent PBM treatment at 30 J/cm² (L30) and diabetic group that underwent PBM treatment at 90 J/cm² (L90). The induction of DM was carried out according to the experimental model of administration of streptozotocin (STZ) into the penile vein of the animals. PBM treatment started 15 days after STZ injection and the irradiation was performed at 2 points, at the abdomen, with a total of 3 consecutive sessions. The intraperitoneal tolerance test for insulin (ipITT) and glucose (ipGTT) was performed. At the end of the experimental period, rats were euthanized, and the pancreas were removed for histological analysis and immunohistochemistry of insulin and 8-OHdG. The evaluation of body mass demonstrated a lower loss for L90 compared to the other groups. Moreover, when the ipGTT and ipITT values in the different groups were compared, there were no differences between them. In conclusion, the higher fluence (L90) of PBM used in this study resulted in a decrease of weight loss in the diabetic animals (which is an important anticatabolic effect).