The seasonal migration of the hagfish, Eptatretus burgeri, was studied in the sea near the Misaki Marine Biological Station of University of Tokyo during the period from October 1970 to October 1975. The hagfish was caught by a cylindrical trap (80 cm in length, 15 cm in diameter) with a funnel-shaped one way entry at both ends. Sardines were used for baits. The hagfish were found in water of 6 to 10 m depths in Koajiro Bay and Moroiso Bay near the Station from mid October to mid July of the following year, but they were absent from the bays at other times. On the other hand, they were found throughout the year in offshore water of 50 m depth, about 1,600 m west of the Station. Two hundred and nine hagfish caught in water of 50 m depth in October and November were marked by making a small triangle cut on the tail fin and releasing them at the original place of capture. Sixty five marked hagfish in total (31.1%) were recaptured in Koajiro Bay and Moroiso Bay. Among 1,323 hagfish marked in Koajiro Bay in April, May and June, 23 marked hagfish (1.7%) were recaptured in water of 50 and 100 m depths. The mean total lengths of the hagfish collected in Koajiro Bay and water of 50 m depth during November through April were 43.3± 0.7 cm (± SEM, n=1,796), and 34.3± 0.9 cm (± SEM, n=689), respectively. Data on monthly collections of the hagfish in both Koajiro Bay and water of 50 m depth indicated that when they migrate from shallow to deep water and the reverse, larger hagfish more than 39 cm in total length move first being followed by smaller ones, but many hagfish less than 35 cm in length remain in water of 50 m depth throughout the year. We failed to collect either fertilized eggs or juveniles by net sweeping of the bottom of water of 40 to 110 m depth. Furthermore, we could not find hagfish less than 20 cm in either shallow water or water of 50 m depth. It seems that the spawning ground of E. burgeri may not be at the 50 m depth but at a deeper place than 100 m depth. Finally, the present study demonstrated directly the seasonal migration of the hagfish, E. burgeri, between shallow and deeper waters of Sagami Bay by the marking experiments.