ABSTRACT: We examined the diel vertical migration of squid (dorsal mantle length 21 to 490 mm) in warm core ring (WCR) and cold water mass (CW) areas in the transition region of the western North Pacific. A total of 28 squid species belonging to 23 genera, 2 octopus species from 2 genera, and 1 vampyrmorph Vampyroteuthis infernalis were captured from depths of 20 to 700 m by day and night sampling using a commercial otter trawl. Three patterns of diel vertical migration were recognized for 11 of the squid species. (1) Migrant, in which day and night habitats are clearly separated with peak abundance deeper than 300 m during the day and shallower than 300 m at night: Gonatopsis borealis, Gonatus berryi, Gonatus onyx, Eucleoteuthis luminosa, Onychoteuthis banksii, Enoploteuthis chunii, and Watasenia scintillans. (2) Semi-migrant, in which part of the population migrates to the upper 100 m at night from its daytime habitat of 500 to 600 m, while the remainder of the population mainly remains in the daytime habitat: O. borealijaponica. (3) Non-migrant, in which the habitat is consistently distributed below 400 m: Histioteuthis dofleini, Belonella borealis, and H. inermis. Horizontally, E. luminosa, E. chunii, and H. inermis were restricted to the WCR, while other species were distributed in both the WCR and CW areas in the transition region. Among the vertically migratory and semi-migratory species, nighttime distribution depth was similar between WCR and CW for O. banksii, but was deepened by upper layers of warm subtropical waters in the WCR for G. borealis, G. berryi, W. scintillans, and O. borealijaponica. We also examined day–night habitat temperature ranges for these 11 species.