In the automotive industry, the Resistance Spot Welding(RSW) has been applied for many years In order to reduce the vehicle's weight and production costs. Typically, a car body contains about more than 4300 spot welds joining sheets of different thicknesses for making just one car and this trend is expected to be continued. However, There are not many Methods to inspect the resistance spot weld. Although measurement of Tensile shear strength and nugget diameter is widely used, another method which is more efficient is required for time and cost savings. The scope of the present study was to find out the most effective approach to non-destructive evaluation of resistance spot welding. Three different techniques such as Photo infrared thermography, Ultrasound-infrared thermography and Lock-in methods were used to acquire information for evaluation of weld soundness. Through experiment, we were able to obtain infrared images and then compared the nugget size with using the naked eye. Eventually, we concluded The mean size of the nugget observed by the naked eye showed the difference of about 20% in the mean size of a nugget actually; The mean size of the nugget observed by infrared thermography showed the difference of about 8% in the mean size of a nugget actually.