3-D stereoscopic PIV is capable of measuring 3-dimensional velocity components. It involves a very sophisticated routine during setup, calibration, measurement and data processing phases. This paper aims to verify the 3-D stereoscopic PIV measurement procedures and to prove that the flow entering the diffuser is a fully developed flow. A diffuser inlet of rectangular crosssection, 130 mm x 50 mm is presently considered. For verification, the velocities from PIV are compared with the velocities from pitot static probe and theory. The mean velocity obtained using pitot static probe is 2.44 m/s, whereas using PIV is 2.46 m/s. It thus gives the discrepancy of 0.8. There is also a good agreement between the mean velocity measured by PIV and theoretical value with the discrepancy of 1.2. This minor discrepancy is mainly due to uncertainties in the experiments such as imperfect matching of coordinates between the probe and laser sheet, unsteadiness of flow, variation in density and less precision in calibration. Basically, the operating procedures of 3-D stereoscopic PIV have successfully been verified. Nevertheless, the flow entering diffuser is not perfectly developed due to the imperfect joining duct and the abrupt change of inlet cross-section introduced. Therefore, improvement to the existing rig is proposed by means of installing settling chamber with multiple screens arrangement and contraction cone. © (2014) Trans Tech Publications, Switzerland.