It is reported for the first time that Fourier transform infrared photoacoustic spectroscopy (FT-IR-PAS) spectra of nanocrystalline monoclinic ZrO2 with different particle size. The results show that absorption intensities of Peaks below 1048 cm-l decrease, while those above 1048 cm-l increase. The POsition of some Peaks have red shift as decrease of particle size. Primary explanation is made for these quantum effects. The pressure effect is also observed.