The M1 phases of the Mo–V–Te–Nb mixed-metal oxides are highly promising catalysts for direct propane (amm)oxidation. Nb is beneficial to the activity and selectivity for acrylonitrile, but direct evidence for Nb location is lacking because structural methods cannot distinguish Nb (Z = 41) from Mo (Z = 42). We have employed high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and density functional theory (DFT) to study the Ta (Z = 73) location in a Mo–V–Te–Ta–O M1 phase produced via hydrothermal synthesis, which possesses uniform Ta distribution compared to M1 phases previously synthesized via slurry evaporation. The HAADF STEM and DFT results indicate that Ta predominantly occupies the pentagonal bipyramidal site (S9). Moreover DFT results validate the previous hypothesis that Ta and Nb both prefer the S9 site.