The Shiretoko Peninsula, located at the southernmost point of the Sea of Okhotsk, was registered as a World Natural Heritage in 2005 in recognition of its rich biodiversity and an example of the interaction between marine and terrestrial ecosystems. However, there is insufficient information on its marine biota, which is an essential component of this ecosystem. This study was conducted from 2006 to 2019 to clarify the macroinvertebrate fauna along the shores of the Shiretoko Peninsula. A total of 299 species from 11 phyla were identified, including 118 mollusks, 107 crustaceans, 34 annelids, 24 echinoderms, and 16 species from other taxa, including two species recorded in Japan for the first time [Oregonia kurilensis (Decapoda: Brachyura) and Henricia alexeyi (Asteroidea: Echinasteridae)]. In addition, five species, including one new species of Isopoda, have been firstly reported from Japan based on the material collected by this project. Faunal similarity and biogeographical features differ between the Sea of Okhotsk side and the Nemuro Strait side of the peninsula, probably because of the effects of warm and cold currents, coastal topography, and drift ice pressure on the shore in winter. The macroinvertebrate fauna of the Shiretoko Peninsula is located at the boundary of different marine biogeographic provinces and is organized by environmental factors unique to the Sea of Okhotsk. Therefore, it is important to monitor the marine biota around the peninsula shores as these species act as bioindicators of environmental changes.