In this study, the friction factors of unsteady pipe flows have been experimentally investigated. The normal temperature water was used as working fluid and pulsating flow superposed on the steady turblent flow, having the variation of velocity approximately represented by sine curve, was used. In the result, the time mean friction factors of the unsteady flow agree with that of steady flow, and the momentary friction factors in the accelerating state are smaller and in the decelerating state larger than that in steady flow for each Reynolds numbers.