The bivalve mollusks Crenomytilus grayanus (Dunker, 1853) and Modiolus kurilensis F. R. Bernard, 1983 are Pacific, Asian species, are mass representatives of the epifauna upper sublittoral coastal waters of Peter the Great Bay (Sea of Japan). C. grayanus is a traditional, and M. kurilensis is a promising commercial species, their resources are significant.The aim of the work–relative analysis of the spatial distribution and biomass of C. grayanus and M. kurilensis on different types of bottom sediments and depths of habitation in Peter the Great Bay. The research was carried out in 2007–2019 by scuba-diving methods of hydrobiological research at the depths of down to 20 m. In total, the data were analyzed for 5,911 stations; Mytilidae were found at 1,635 stations.In mytilids, the vital weight of each individual and average biomass. The landscape diversity of the bottom of Peter the Great Bay determines the almost ubiquitous distribution of C. grayanus and M. kurilensis, which reflects the good adaptation of mollusks to the conditions characteristic of this part of their area. Monospecific druses C. grayanus prevailason hard and soft bottom sediments (78.6 and 38.2% of the total number of stations with Mytilidae), but mixed druses of both species – onsoft bottom sediments (38.3%).Monospecific druses of M. kurilensis on soft bottom sediments are more common(23.5%), than on hard bottom sediments (8.1%).In Peter the Great Bay the average biomass of C. grayanus on hard bottom sediments is 728 ± 47 gm-2, varying from 524 g·m-2 (Amur Bay) to 922 g·m-2 (eastern part of Peter the Great Bay); on soft bottom sediments–491 ± 51 g·m-2 (from 228 g·m-2 in the Ussuri Bay to 829 g·m-2 in the Amur Bay), with the exception of the southwestern part of Peter the Great Bay and Boisman Bay, where this indicator was below 50 g·m-2.The average biomass of M. kurilensison hard bottom sedimentsis 370 ± 74 g·m-2, varying from 18 g·m-2 (Baklan Bay) to 656 g·m-2 (Empress Eugénie Archipelago water area); on soft bottom sediments– 335 ± 37 g·m-2, from 77 g·m-2 (southwestern part of Peter the Great Bay) to 456 g·m-2 (Amur Bay), with the exception of Boisman and Baklan bays, where the species was rare.In Peter the Great Bay the maximum average biomass of each species were noted at depths of 1-10 m (C. grayanus– 664-805 g·m-2, M. kurilensis– 347-485 g·m-2), with increase ofhabitat depth, the abundance of both species decreases. The average biomass of C. grayanus depth of habitat of 10 to 20 m on hard bottom sediments, are also quite high (431-507 g·m-2).On soft bottom sediments, with a change in depth from 10-15 to 15-20 m, it’s average biomass decreases from 204 ± 33 to 27 ± 11 g·m-2.The average biomass of M. kurilensisdepth of habitat of 10-15 m is 121-194 g·m-2, and at depths of 15-20 m - 11-60 g·m-2 on both types of bottom sediments.