Intensive sampling was carried out in the marine environment of Mumbai and Jawaharlal Nehru ports to investigate the composition of benthic sessile population on three different occasions during 2001 to 2002. this study recorded 29 species of hard substratum fauna and 14 associated fauna. The acorn barnacle Balanus amphitrite and tube dwelling polychaete Protula tubularia were the dominant hard substratum species recorded from the area. Protula tubularia with no previous records from Indian waters appears to be an introduction in the region. The bivalve Mytilopsis sallei, which has been reported earlier as an invasive species Indian waters, was mostly found restricted to enclosed habitat within the ports. A comparison with historic data, based on the literature available, indicates the presence of 15 taxa which appeared for the first time this locality the present study envisages that the hard substratum faunal composition in Mumbai harbour environment is changing due to ever increasing human perturbation.