The degree of polarization of skylight in the zenith direction before and after the eruption of the Mount Pinatubo observed with a newly developed multiwavelength photometer as well as the profiles of backscattering ratio detected by a lidar are used along with a Monte Carlo radiative transfer model to evaluate the optical depth of stratospheric aerosols at 0.7-μm wavelength over Beijing (39¿57'N, 116¿21'E). Observations show that the stratospheric aerosols over Beijing significantly increased after the eruptions of the Mount Pinatubo. A large temporal variation was found. The optical depth of the aerosols reached the maximum during the period from February 1992 to April 1992, then decreased gradually. Although significantly decreased, the optical depth of stratospheric aerosols had not recovered to the background level until September 1992. The retrieved results show that there was a layer of aerosols in the layer 8--11 km with an optical depth of 0.01 after the eruption. This layer of aerosols may interfere with the deduction of the aerosol backscattering ratio from the lidar detection and might also affect the formation of ice crystals in cirrus clouds and therefore influence the climate. ¿ American Geophysical Union 1993