Aerosol spectral optical depths were measured over Arabian Sea as a part of the Arabian Sea Monsoon Experiment (ARMEX). These are the first measurements of aerosols over northern and central Arabian Sea during Indian summer monsoon season. Aerosol visible optical depths were in the range of 0.4 to 0.7 with Angstrom wavelength exponent of ~0.35 and single scattering albedo of ~0.97 indicating the dominance of large non-absorbing aerosols. Aerosol optical depth increases exponentially with sea-surface wind speed. Our estimates show that sea-salt contributes ~60% to the composite aerosol optical depth. The presence of aerosols over Arabian Sea during summer monsoon season decreases the short wave radiation arriving at the surface by as much as 21 W m-2 and increases top of the atmosphere reflected radiation by 18 W m-2.