The research is to assess the uncertainty of aerosol optical depth (AOD) and Ångström exponent products retrieved from the Multi-angle Imaging SpectroRadiometer (MISR) data by means of comparing them with ground measured data in Hong Kong in the period of 2005 to 2013. Further analysis of how these uncertainties are spread into the calculation of UV Index (UVI) is conducted based on a radiative transfer model. The results indicate that the maximum values of UVI uncertainty caused by MISR/AOD uncertainty are 0.55 and 0.36 in summer and winter, respectively. The maximum of UVI uncertainty caused by Ångström exponent uncertainty are 0.13 and 0.11 in summer and winter, respectively. Compared with the UVI exposure grades put forward by the World Health Organization, the uncertainty of both AOD and Ångström exponent can cause at most one grade deviation in the worst situation. In this sense, MISR/AOD and Ångström exponent products are reliable as input in the calculation of UVI.