Bio-logging systems are a useful tool for understanding the behavior of marine mammals and their environmental conditions.In particular, accelerometer data provide characteristic information on feeding events, posture and body movement of the animals. Naito et al. (2010) reported on acceleration patterns of feeding behavior and unknown acceleration patterns of jaw motion of two free-ranging adult female Weddell seals (No. 06 and No.16) instrumented in Atka Bay (70º39’S, 08º15’W) in early December 2008. Although acceleration pattern of feeding behaviour was inferred by data obtained from the feeding experiments of captive seals, acceleration pattern of non-feeding behaviour has never been examined in detail. Here we re-examined those data【depth (±0.1m), environmental temperature (±0.1℃), and two way acceleration, heave(x) and surge (y) data at 32Hz were measured over three days】to obtain new insight into the behaviour of the species. We detected low frequency cycle with attenuating pattern from two adult female Weddell seals. Individual (No.06) and (No.16) showed average cycle of 0.217±0.007 sec. and 0.161±0.008 sec., average duration of 4.43±0.225 sec. and 4.08±0.68 sec., and average depth of 2.06±0.42 m and 6.21±1.19 m, respectively. We isolated 135 events in 269 dives of the seal (No.06) and 29 events in 167 dives of the seal (No.16). It is well known that Weddell seals produce a number of vocalizations at shallow depths during breeding season and these vocalizations assumed to be related to mating behaviour. However, frequency of our data was lower than that of usual vocalization. Although the function of this low frequency pattern is still unknown, we hypothesize that low frequency pattern emitted by shivering some parts of lower jaw (or laryngeal organ) have an unknown function like “social call-interaction” during the breeding season.