A novel velocity measurement method for microscale flow field characterization is reported, particle linear image velocimetry (PLIV). The method records a series of one-dimensional images that represent the trace of particles in the flow across a one-dimensional imager. Linear imaging results in a faster frame rate than planar imaging, allowing observation of larger microscope magnification or measurement of faster flow rates in real-time than comparable techniques. In contrast to particle image velocimetry (PIV), PLIV does not require high-speed cameras or shutters. Furthermore, PLIV is adaptable to multiple linear imager formats and, as one example, can use laser scanning confocal microscopes (LSCM) that acquire images slowly but with high spatial resolutions and optical sectioning ability. Higher resolution can be obtained for flows where in-plane velocity gradient in the direction of the optical path (z-direction) is important. This paper presents the PLIV algorithm, and demonstrates its utility by measuring Poiseuille flow with 1-μm resolution in a microfluidic environment.