Abstract: The particle size of nano iron phosphate powder was experimentally measured with Zetasizer Nano S90 laser particle size analyzer.The effects of the factors， such as kind and dosage of dispersant，ultrasonic time，and content of iron phosphate particles in solution，on powder′s dispersive property and the measurement results were examined.The optimum analysis conditions were confirmed as follows: distilled water as the disperse medium，the sodium dodecyl sulfate mass concentration was 1 g/L（dispersant），the nano iron phosphate mass concentration was 0.2 g/L，and the ultrasonic time was 15 min.The measured results of laser particle size analyzer were basically in correspondence with that of scanning electron microscopy.

Key words: laser particle size analyzer, nano powder, iron phosphate, particle size