  The lacunarity is an interesting property of a formal series. We say a series
is lacunary if "almost all" of its coefficients are zero. In this article we
considered about the lacunarity of some eta-products like \eta(z)^2\eta(bz)^2,
and proved that they are lacunary if and only if b is 1,2,3,4 or 16. Then We
write them as linear combinations of some CM forms.
