Grain size parameters of lake sediments are common environmental proxies in lake sediment and environ-menta] change study. With the development and widely use of laser diffraction particle size analyzer in recent years, the application of grain size proxies was advanced while the precision and efficiency of grain size measurement were also improved. However, the results of one sample may be having some difference by using different types of laser diffraction particle size analyzers. Here we report a case study of two lake sediment cores from Nam Co in Tibet using two familiar laser diffraction particle size analyzers. Seen from the repeatedly measurement results of the same sample, Mastersizer2000 manufactured by Malvern Instruments is better than LSI 3320 by Beckman Coulter, while LSI3320 is better than Mastersizer2000 in the detective effect of relatively fine and coarse particles with rather few content. The grain size parameters d(0.1) and d(0.5) obtained by two instruments are rather similar in the variation trend as well as the absolute values, whereas the d(0.9) has rather big difference. The comparative results of this study can provide base on extracting paleoenvironmental information by using grain size parameters of lake sediments.