Gear resistance is an important mechanical aspect to ensure the proper functioning of power transmission systems. In general, gear design is based on both geometry and material parameters and, in many cases, surface treatments are required to guarantee the desired mechanical properties. It is well known that one of the most dangerous failures in gears refers to tooth root fillet cracks, caused by bending fatigue. In general, mechanical parameters involved in fatigue resistance for materials or components, such as bending fatigue limit, are evaluated by means of dedicated experimental campaigns. Standards help engineers in the gear design phase by providing material resistance data arranged on the basis of chemical composition, manufacturing process and surface treatment. This approach requires significant time and effort from the experimental point of view to obtain limited and unlimited life curves (S-N diagram), which are essential for the evaluation of the bending fatigue resistance of the gear under consideration. Regarding the experimental campaigns, bending fatigue tests may be performed following two classical approaches, Meshing Gears (MG) and Single Tooth Bending Fatigue (STBF) tests. In this work, the STBF approach was adopted in combination with a Thermographic monitoring. This way, a full superficial acquisition of the tooth root thermal emission was performed during the fatigue test at different loads. So, the fatigue limit was estimated from an iterative analysis of thermal parameters evolution (Two Curves Method, TCM). The proposed Non- Destructive Thermographic approach (TCM), already well-established in the literature for classical samples, allowed in this work to obtain fatigue limit data in the specific case of gears. Gears made of C45 and 20MnCr5 with surface treatments as induction hardening and case hardening respectively were tested. The obtained results in terms of bending fatigue limit values were compared with those evaluated by using consolidated approaches as the Stair Case Method and with the indications available in ISO 6336 Standard for that material.