This paper presents the characteristics of hydrodynamically focused streams to be used in Microscale Particle Image Velocimetry (micro-PIV). The investigation was done by means of Confocal Laser Scanning Microscopy (CLSM) in channels of cross-sections 260 x 200m and 1040 x 800 m, within the downstream velocities range from 0.1 to 2.5 cm/s. The formulation of a curvature of the sheet, its dependence on the side stream ratio, and the over all downstream velocity are discussed qualitatively and quantitatively. The results show that the curvature is highly dependent on the velocities of the system. Sheet characteristics such as curvature and observed sheet width variation become amplified with higher velocities. This leads to the conclusion that hydrodynamic focusing is promising as a selective seeding technique for use in micro-PIV up to velocities of few cm/s. However, the fact that this is the upper velocity range in microfluidics renders the SeS-PIV technique as a very suitable tool for complicated flows visualization.