We carried out an aerial survey to estimate the abundance of finless porpoises Neophocaena phocaenoides off the Pacific coast of eastern Japan between Sendai Bay (38°23’N) and the mouth of Tokyo Bay (35°13’N) in May and July 2000. In this region, almost nothing is known about the status of this species. Thirty-seven east-west transects (707.0 km in total) were flown at intervals of 11.1 km. A total of 59 animals (37 primary sightings) was observed along the transects.Although the finless porpoises in this area have been assumed to constitute a single population, two distributional gaps at around 35°N and 37°N suggest the possibility of population subdivision. Finless porpoise sightings were not restricted by distance from the coast, but by water depth (<40 m).The density and abundance of finless porpoises in the area from Sendai Bay to the east coast of Boso Peninsula were tentatively estimated at 0.502 animals/km2 and 3,387 animals (CV = 32.7%),respectively. This density was lower than in other areas around Japan.