The study on species diversity of macrobenthos in seagrass bed at Nha Trang Bay was carried out in 2010. A total of 163 taxa belongs to 88 families were found. of which Polychaeta was the richest species group (89 taxa), Mollusca, Crustacea and Echinoidermata with 33, 32 and 9 taxa. This study added 17 species comparing with the results of 2003 and 2006. Using NaG/SA Protocol to study macrobenthos community, the result showed the difference of number of species, density of species and dominant species between 2 sites as well as 2 types of seagrass beds (monospecies and multispecies). The density of macrobenthos individual were 10.488 ind/m2 in Dam Tre site, 2 times higher than those in Dam Gia site. Some macrobenthos groups decreased of number of species by time. Dam Gia had 97 species and Dam Tre had 112 species in 2006 but in 2010 the number of species in Dam Gia were 75 and 74 in Dam Tre. The species of mol/use group reduced from 53 to 18 between 2006 and 2010. The main reason is the impact of infrastructure building activities for tourist area.