Epitaxially strained NaNbO3films were grown by liquid-delivery spin metal–organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO3films on NdGaO3exhibit the orthorhombiccphase. With increasing in-plane strain a first structural phase transition to the monoclinicrphase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to theaaphase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Diéguez, Rabe & Vanderbilt [Phys. Rev. B, (2005),72, 144101] for NaNbO3films.