This paper presents the design consideration of a low-profile LLC resonant converter using tw,o flat transformers. The trend toward high power density, high efficiency, and low profile in power supplies has exposed a number of limitations in the use of magnetic component structures. The LLC resonant converter can be operated at a high switching frequency with high efficiency because the switching loss is reduced by soft-switching. However, flat transformer loss causes problems at a high switching frequency. As a result, temperature of flat transformers becomes high. Therefore, it is necessary to reduce the transformer temperature by analyzing the loss. In this proposed converter, flat transformer is integrated into advanced power conversion application systems. Low-profile power module of profile of about 14mm is achieved. Temperature inside of transformer repressed to 61C and an overall efficiency of about 97.8% was obtained.