Two kinds of nanopowders were studied. One is NiFe2O4 spherical nanopowders which have different particle sizes. Another is ZnO nanopowders including two series of spherical particles and tetrapod nanowhiskers. Through measuring the infrared diffuse reflection spectra of nanopowders, it can be found that the particle size and morphology affect the infrared diffuse reflection spectra. For the NiFe2O4 nanopowders the smaller the particle size, the larger the K-M value. And when the particle size is large enough , the effect of the particle size on infrared diffuse reflection spectra would disappear. For the ZnO nanopowders the effects of the particle size and morphology are more special. The effect of the particle sizes of tetrapod whisker nanopowders on infrared diffuse reflection spectra is more than that of spherical nanopowders.