Extensive and collocated measurements of aerosol optical depths (AODs), mass concentration of composite aerosols and aerosol black carbon (BC) were made over the Bay of Bengal (onboard R/V Sagar Kanya during its cruise #197) region during post-Indian summer monsoon period. These data along with MODIS (onboard TERRA satellite) data shows that aerosol visible AODs were in the range of 0.2 to 0.7 (with mean value of 0.43 ¿ 0.12) and Angstrom wavelength exponent of ~0.93 ¿ 0.21 which in conjunction with a single scattering albedo (ω) of ~0.94 indicates the presence of weakly absorbing aerosols. The BC mass fraction was ~2.9 ¿ 1.1% during post-monsoon season compared to 5.8 ¿ 0.6% (with ω of ~0.88) during pre-monsoon season. The presence of aerosols over Bay of Bengal during post-monsoon season decreases the short wave radiation reaching the surface by as much as 25 W m-2 and increases top of the atmosphere reflected radiation by 14 W m-2.