Self-polarization (or unipolarity) is often observed in thin ferroelectric films. It may be caused by different physical reasons such as:  - polarizing effect of electric field which is caused, for instance, by space charge localized near bottom (or top) electrode of thin-film ferroelectric capacitor,  - reorientation effect in the substrate plane due to linear mechanical stresses appearing as a result of difference in linear expansion coefficients or lattice parameters of the substrate and the film,  - nonlinear mechanical stresses leading to bending the system film/substrate (flexoelectric effect) [1-4].  To date, the mechanisms of spontaneous formation of macroscopic poled state is best studied in thin PbZr1-xTixO3 (PZT) films. However, the reasons that lead to a particular orientation of the selfpolarization vector, are far from understanding, as well as the reasons for which the vector direction can be changed to the opposite one when changing the conditions for the formation of thin PZT films. In the work, to study the reasons of reorientation of self-polarization vector, thin polycrystalline PZT films were grown by RF magnetron sputtering depending on working gas (Ar + O2) pressure and the temperature of perovskite phase crystallization. The films were fabricated in two stage process on Pt/TiO2/SiO2/Si substrate. At the first stage, films were deposited at low substrate temperatures (~150^oC) and, at the second stage, ones were annealed and crystallized into perovskite phase at 580-650oC in the conventional furnace. The film thickness was varied from 500 to 1000 nm.  The structural, ferroelectric, pyroelectric and piezoelectric properties of the films have been studied. Microstructure and composition of the films were studied using scanning electron microscope EVO-40 (Zeiss) and atomic force microscope Smena (NT MDT, Zelenograd). Piezoelectric contact mode (applied alternative voltage 0.25 V) was used to fix piezoelectric response in the films under study. The dynamic method of pyroelectric measurement with periodic rectangular pulses of heat flux was used to evaluate pyroelectric properties of the films. IR laser CLM-1845IR-980 (  λ= 980 nm, P = 220 mW) was the heat flux source for this measurement. Modulation frequency of the infrared radiation varied in a range from 5 Hz to 1 kHz.  The experimental results have shown the change of orientation of self-polarization vector observed as at increasing annealing temperature, as at increasing gas pressure from 2 to 8 Pa on stage of film deposition. In both the cases, it is revealed the change in atomic ratio of Pb and (Ti+Zr) depending on gas pressure and annealing temperature. The results suggest the “electrical” nature of selfpolarization and changing donor to acceptor charge carriers in the films.