In this paper, the characteristics of Mega-Flux® and JNEX® cores are compared to the inductor of buck-boost converter for Hybrid Electric Vehicles (HEVs). The core losses were measured at various flux densities at 15kHz and the magnetic simulations of Mega-Flux® core were fulfilled. Magnetic simulations were tried in terms of magnetic flux saturation level, AC copper loss due to flux leakage and temperature rise at the condition of the water coolant of 50 degrees Celsius. Similar operating tests with HEVs dc-dc converter were fulfilled with established 40kWatt dc-dc converter system. Under the specifications of boost converter for 40kW, the power inductors were designed with Mega-Flux® core, JNEX® core and the experimental results were provided with the respect of dc bias characteristics, temperature rise and acoustic noise of the inductor.