Micro fluid mechanics is one of interesting fields in modern fluid mechanics, because it is applied to physical, industrial, and biological research. In the present study, pressure drops were measured for some kinds of liquids passing through various micro orifices at low Reynolds numbers. It was found that the measured pressure drops almost agree with the prediction by Navier-Stokes equation for orifices smaller than or equal to 50 micron meters in diameter for water and glycerol aqueous solution, but they increase over the prediction for orifices of 100 and 200 micron meters in diameter. Dimensionless pressure drops appear not to be correlated with Reynolds number for some surfactant solutions.