Interannual variability of the 5-day wave in the stratosphere is examined by the use of National Center for Environmental Prediction reanalysis data. Quasi-biennial variation of the 5-day wave amplitude is clearly seen in the stratosphere. This quasi-biennial variation is closely related to the zonal wind variation associated with the equatorial quasi-biennial oscillation in the stratosphere. We give a short description of the mechanism bringing about the relationship.