A model catalyst system of Pt nanoparticles (2–5 nm) dispersed on γ-Al₂O₃ (111) was prepared to study the support effects on nanoparticles shape and structure by cross-sectional high-resolution electron microscopy. A dewetting equilibrium shape of Pt nanoparticles was observed with a low-index plane orientation relation: Pt(111)[211]∥γ-Al₂O₃(111)[211] and Pt(100)[011]∥γ-Al₂O₃(111)[211]. Lattice-matching epitaxy of Pt(110)∥γ-Al₂O₃(110) was found across their interface to maintain a minimum interface strain during particle growth. To quantitatively interpret the interfacial energy and adhesion energy of the nanoparticles, the Wulff–Kaischew theorem was applied by taking into account the γ-Al₂O₃ support modifications to the equilibrium shape of nanoparticles. The present approach quantitatively solved the adhesion energy of the particle/support and could help to interpret nanoparticles equilibrium shape and stability.