The phase transformation of alpha'-NaV2O5 has been studied by electron diff
raction. It has been observed for the first time that two different types o
f diffuse scatterings exist; one appears slightly above T-c and the other a
ppears already at room temperature. The former type of diffuse scattering l
ocks into superlattice reflections at T-c. The superlattice reflections and
the former type of diffuse scattering are explained by a long-period anti-
phase-domain structure (LPAPDS) model and the fluctuation of its period.