Anisotropic oxidation of crystallites of vanadyl pyrophosphate ((VO)(2)P2O7) has been demonstrated by Raman spectroscopy with samples having different microstructures. Oxidation of these samples by O-2 produced X(1) phase, alpha- and beta-VOPO4 phases. The relative peak intensity of the X(1) phase to the other phases correlated well with the ratio of the (100) plane to the side planes (surface area-basis). This correlation showed that the (100) plane was oxidized to X(1) phase and the side planes to alpha- and beta-VOPO4. For example, thin plate-like (VO)(2)P2O7, of which the (100) fraction is 98%, was oxidized almost exclusively to X(1) phase. But when it was fractured into small plates to increase the side planes and then oxidized, alpha- and beta-VOPO4 were detected in addition to the X(1) phase. These results are consistent with our previous conclusion that the (100) plane of (VO)(2)P2O7 is selective, but side planes are nonselective for catalytic oxidation of n-butane.