Abstract: The flow fields of ultramicro rotary fluid fragmentor were measured and inves-tigated by using laser Doppler anemometer.Some flow parameters, such as mean velocity,fluctuating velocity distribution,flow patterns,shear rate and Reynolds stress were obtained.The charicteristics of the flow field were determined.The primary principles of fragmentingthe particles were analyzed. Some useful information was provided for industries of ultrami-cro rotary fluid fragmentors.