Based on HYbrid Coordinate Ocean Model (HYCOM) assimilation and observations, we analyzed seasonal variability of the salinity budget in the southeastern Arabian Sea (AS) and the southern part of the Bay of Bengal (BOB), as well as water exchange between the two basins. Results show that fresh water flux cannot explain salinity changes in salinity budget of both regions. Oceanic advection decreases salinity in the southeastern AS during the winter monsoon season and increases salinity in the southern BOB during the summer monsoon season. In winter, the Northeast Monsoon Current (NMC) carries fresher water from the BOB westward into the southern AS; this westward advection is confined to 4°-6°N and the upper 180 m south of the Indian peninsula. Part of the less saline water then turns northward, decreasing salinity in the southeastern AS. In summer, the Southwest Monsoon Current (SMC) advects high-salinity water from the AS eastward into the BOB, increasing salinity along its path. This eastward advection of high-salinity water south of the India Peninsula extends southward to 2°N, and the layer becomes shallower than in winter. In addition to the monsoon current, the salinity difference between the two basins is important for salinity advection. Based on HYbrid Coordinate Ocean Model (HYCOM) assimilation and observations, we analyzed seasonal variability of the salinity budget in the southeastern Arabian Sea (AS) and the southern part of the Bay of Bengal (BOB), as well as water exchange between the two Results show that fresh water flux can not explain salinity changes in salinity budget of both regions. Oceanic advection decreases salinity in the southeastern AS during the winter monsoon season and increases salinity in the southern BOB during the summer monsoon season. Monsoon Current (NMC) carries fresher water from the BOB westward into the southern AS; this westward advection is confined to 4 ° -6 ° N and the upper 180 m south of the Indian peninsula. Part of the less saline water then turns northward, decreasing summer in the southeastern AS. In summer, the Southwest Monsoon Current (SMC) advects high-salinity water from the AS eastward into the BOB, increasing salinity along its path. Th is eastward advection of high-salinity water south of the indian peninsula extends southward to 2 ° N, and the layer becomes shallower than in winter. In addition to the monsoon current, the salinity difference between the two basins is important for salinity advection.