Epitaxial thin films of lanthanum nickel oxide Ruddlesden-Popper series (Lan+1NinO3n+1) have been prepared on different single-crystal substrates by metal organic chemical vapor deposition. Varying the La/Ni composition ratio in the precursor solution allows deposition of films with controlled La/Ni stoichiometry ranging between 1 and 2. Epitaxial La 2NiO4 (n = 1) and LaNiO3 (n = ∞) pure phases were obtained for La/Ni close to 2 and 1, respectively. For intermediate La/Ni composition, films with a microstructure consisting of a disordered stacking of nanodomains with progressively increasing average n value were obtained. Similarly with bulk samples, the electronic conductivity of the nanostructured films increases with the measured average n value, opening the possibility to prepare new mixed ionic and electronic conducting nanocomposite thin films with tailored properties © 2007 American Chemical Society.