Abstract: This paper presents a micro flow cytometer with a 2D hydrodynamic focusing and a micro-weir effect capable of concentrating particles/cells in the center of a sample stream for high-precision particles/cells counting.A simple and reliable isotropic wet etching fabrication process is used to fabricate the micro-weir structure in the cytometer on soda-lime glass substrates.The present micro flow system integrates three major modules,namely a hydrodynamically driven flow cytometer,a micro-weir structure in microchannel,and a laser induced fluorescence for particles/cells detection purposes.The results shown experimentally and numerically that particles/cells can be squeezed hydrodynamically into a narrow stream by two neighboring sheath flows and separated particles in vertical direction by micro-weir structure that they particles/cells individually through a detection region.The experimental and numerical results confirm the suitability of the proposed device for applications requiring the high-precision counting of particles or cells within a sample flow.