Two wavelengths and depolarization technique in lidar measurement were applied to aerosol layers near the tropopause to estimate the characteristics of size distribution and shape of aerosol particles. The method of analysis of depolarization data was improved to be effective to optically thin and thick aerosol layers. The results taken by these techniques showed that the layers consisted of small and non-spherical particles. We discuss a procedure to correct the effects of non-sphe-ricity and changes of the refractive index of aerosol particles on the data analysis. We also discuss the origin of the particles and the influences on the generation of upper level clouds on the basis of the measurements.