Potassium tantalate niobate [K(Ta1−x Nb x )O3 or KTNJ films were deposited by pulsed laser deposition (PLD) on (100)MgO substrates from targets of KTN with x=0.45. The effects of substrate temperature (300–700°C) and ambient oxygen pressure (50 and 300 mTorr) on the characteristics of films were investigated. At 500°C and 300 mTorr, films were amorphous with a few isolated, randomly-oriented crystalline grains of perovskite and pyrochlore. At 600°C and 300 mTorr, the films comprised a columnar microstructure consisting of a mixture of amorphous phase with (100) perovskite. At 650°C, films were almost entirely (100) perovskite. At 700°C, the films were predominantly (100) perovskite, but contained a much higher fraction of pyrochlore. At 50 mTorr, pyrochlore was found in significant fractions up to 650°C. At 700°C, films were predominantly (100) perovskite. Rutherford Backscattering analysis of the chemical composition showed that all the films were potassium-deficient and the tantalum to niobimn ratio exceeded that found in the targets for all deposition conditions. There appeared to be a relationship between oxygen pressure during deposition and the amount of potassium retained in the films.