Richness, diversity and evenness of decapod crustaceans off Mumbai coast based on sampling during October 2002 to January 2003 are reported. The richness estimated by Margelaf and Menhinick indices gave contrasting values of 0.86 and 0.23, respectively, with the same sample size. Simpson and Shannon diversity indices were 0.49 and 1.07, respectively. The evenness was studied using five different indices and the results were analysed for the sensitivities of the indices with the number of species in the sample. Hill diversity numbers of different orders were in units of effective number of species in the sample. The Ranked Species Abundance curve showed the clear dominance of some species over others.