The degradation of air quality is a consequence of the fast-growing rates in the urban areas and has harmful effects on human health. It is known that the aerosol particles are important contributors to the atmospheric energy budget, cloud properties and atmospheric chemistry. There is still a large uncertainty in estimating the global aerosol total (direct and indirect) effect on the climate, and the uncertainty is even larger in understanding the urban pollution effect on local or global climate. The MODIS sensor algorithm of aerosol optical properties over continent brought a new light to the monitor of aerosols from urban areas. The current operational product with 10 km x 10km is focused on the climatic effects of the global aerosol distribution. The analyses of aerosol distribution over an urban area require a higher spatial resolution. This work explores the use of MODIS in the retrieval of AOD over urban areas with higher spatial resolution. Aerosol Optical Depth (AOD) was retrieved with 1.5x1.5 km resolution over the megacities Sao Paulo, Mexico City and Beijing in a long time series (2002-2005). The products were compared with the CIMEL from the AERONET Global Aerosol Robotic Network. Advantages and limitations have been analyzed in the methodology. This study analyze the aerosol optical properties such as single scattering albedo, asymmetry parameter and size distribution and compare between the different sites of measurement. The MODIS AOD products with finer spatial resolution generated in a systematic way is a powerful tool to complement the ground-based monitoring stations measurements.