Due to its appreciable electro-optical properties, potassium tantalate niobate (KTN) thin films of high quality are expected to enhance the functionality of integrated photonics optical modulators. Unfortunately, they are inherently hard to synthesize. Herein, the authors present atomic layer deposition (ALD) of oriented KTN for the first time. They study the variability in phase content with respect to potassium concentration across a variety of substrates. Films grown with a slight overstoichiometry in potassium show excellent crystal quality of a pure perovskite phase. Highly oriented films were obtained on substrates of a similar lattice constant to bulk potassium tantalate niobate. Nearly stoichiometric potassium contents yield films with similar quality, albeit with trace amounts of pyrochlore. Potassium deficient films consist of an overwhelming amount of pyrochlore. Phase control and orientation control are essential when considering device integration of optical modulators. The authors believe that ALD is an ideal technique to obtain KTN thin films with high growth control.