Thin films of ferroelectric materials have attracted great interest for various applications, including non-volatile memory, infrared sensors, optical switches, and ultrasonic transducers. The perovskite sodium-potassium niobate is a material that has been known due to its ferroelectric and piezoelectric properties. Depending on growth conditions, thin films of (Na,K)NbOx (NKN) show high piezoelectric and dielectric constants, low losses (tan 8), and tunable properties, which makes them suitable for applications such as phase shifters, tunable filters and resonators, and electronic circuits. The aims of this work were to obtain a better understanding of the relation between process conditions, microstructure, and physical properties of NKN films and to optimize their electrical-, and mechanical properties. The results have contributed to understand the effects of deposition parameters, such as partial pressure of gases, argon and oxygen, and growth temperature on chemical composition and properties of the films.