The quasi-biennial oscillation is fairly well simulated by use of a T21 60-layer general circulation model with moist convective adjustment. The model is the first version of the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) general circulation model. The vertical resolution is approximately 500m in the upper troposphere and lower stratosphere. The damping time for the maximum wavenumber in the fourth-order horizontal diffusion is 20 days, being about one-order of magnitude less than that in standard general circulation models. The period of the oscillation is 1.5 years, which is slightly shorter than that of the observed quasi-biennial oscillation. The simulated oscillation occurs in the middle stratosphere, being slightly higher than that observed in the equatorial lower stratosphere. The amplitude of the zonal-wind associated with the oscillation is 20 ms−1 which is comparable to the observed value.