The frictional wave-CISK interpretation for the origin of the Madden-Julian oscillation is investigated by comparing two simulations with the Goddard atmospheric general circulation model, one with surface friction and the other without. This comparison indicates that without surface friction the MJO can still exist but with weaker intensity. Thus, the frictional wave-CISK interpretation for the origin of the MJO is in doubt. Surface friction, though not necessary for the existence of the MJO, plays an important role of determining the intensity and the dominant period of the MJO