In recent years, the development of car body structures using lightweight materials such as an aluminum alloy has progressed by taking into consideration environmental issues. Laser welding of aluminum alloys has been widely applied due to the commercialization of high-power fiber lasers. The application of welding techniques in actual structures requires a high level of safety and reliability. Thus, it is necessary to evaluate the fatigue fracture behaviors of the welds, which account for the majority of fractures. This study focused on the fatigue limit estimation method based on dissipated energy. The dissipated energy is a small heat generation caused by local plastic deformation. In recent years, the estimation method of fatigue limit by the dissipated energy is being considered for application in the industrial fields through the development of infrared sensors of high sensitivity and lock-in processing. This paper discussed the applicability of the estimation methods of the fatigue limit for the laser welds of aluminum alloys based on the dissipated energy measured using infrared thermography. The laser welds of aluminum alloys were fractured at the boundary between the weld metal and heat-affected zone. The fatigue limit of the laser welds was lower than that of the base metal specimen. In the measurement results of dissipated energy, the estimated fatigue limits of the laser welds and the base metal specimens were consistent with the fatigue limit by the fatigue tests. Thus, the fatigue limit of laser welds of aluminum alloys could be estimated by the dissipated energy.