The main factor that has to be considered in the inductor designing is the power losses occurred in the core and windings, and temperature rise released depend on these power losses. In addition to worsening efficiency, temperature rise due to the power losses reduce lifespan of the isolation materials and cause significant change on electromagnetic behavior of the core. These effects become more important for the high power medium frequency inductors. Therefore, the cooling conditions have to be considered during the designing stage to keep the temperature rise of the inductors at a certain level. In this study, medium frequency inductor of an LCL filter used in the grid interactive inverter output has been designed. The toroidal gapped-core shape has been made up with silicon steel alloy. The core and the winding power losses of the inductor have been determined with finite element analysis (FEA) based co-simulations, and then its thermal behaviors have been investigated with the calculated heat sources for different ambient temperatures.