As a non-intrusive flow measurement technique, particle image velocimetry (PIV) is of intense research interest to those investigating turbomachinery. In most of turbomachinery applications, the complexity of the flow structures requires the use of three-component or stereoscopic PIV and the geometrical scales of the machines require the use of endoscopes in order to access the flow channel. This work presents the development of the endoscopic stereoscopic PIV for flow investigation at the inlet of a process centrifugal compressor. A new image reconstruction method is presented, which is capable of resolving high order distortions of the endoscopic imaging. In order to improve the measurement accuracy, a method for the calibration of pressure and temperature signals under quasi-steady conditions is developed and its application to the flow measurements with the 5-hole pressure probes is presented. Finally, several aspects of the application of the PIV at the inlet of the compressor together with a typical result are presented for the first time.