We work out a theory of the acoustoelectric effect in nanostructures u
nder the ballistic conductance regime. The ultrasonic wavelength is as
sumed to be much smaller than the longitudinal dimension of the micros
tructure. We predict giant quantum oscillation of the acoustoelectric
current under gate voltage variation. By this we mean that the maxima
of the oscillatory part far exceed the minima. The effect can be used
for the investigation of the electron spectrum of microstructures.