La0.7Sr0.3MnO3 (LSMO) thin films have proven to act as an efficient spin injection electrode in hybrid organic/inorganic spintronic devices. Optimal control of the chemical composition of the LSMO outermost layer is a key issue in the realization of efficient and reproducible spintronic devices. Low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS), empowered by density functional theory (DFT) investigations have been used to reveal the chemical composition of the LSMO termination. The topmost layers consist of a Sr- and Mn-rich phase evolving to the bulk phase via a gradual increase of the La content.