In order to downsize the storage unit of Hybrid Electric Vehicles, a novel high step-up interleaved boost converter has been proposed. This converter is suitable for automotive applications due to its expected high voltage gain. However, the actual voltage conversion ratio may be significantly reduced by the parasitic resistance effect of the circuit because the input current tends to be large at a high step-up operation and therefore the voltage drop at the parasitic resistance may not be ignorable. This paper analyzes the effect of the parasitic resistance on the voltage gain and evaluates the result experimentally. Consequently, it is found that parasitic resistance affects the voltage gain largely as the ratio of the number of turns in the integrated magnetic component of the proposed converter increases and particularly when the duty cycle is larger than 0.5.