Seals are supposed to forage in efficient manner during dives due to strict physiological constraints. Understanding of foraging behavior is essential for a comprehensive understanding of overall diving behavior. Although several techniques of measuring feeding behavior have been developed, direct measurement of feeding efficiency has not been made. Simultaneous measurement of feeding rate and effort is essential to study feeding efficiency. In order to develop simultaneous measurement of feeding events and effort (swim stroke) we tested a new mandible accelerometer method on free ranging Weddell seals in the Atka Bay, Eckstroem Ice Shelf, Antarctica in November/December 2008. Before to conduct the field test on Weddell seals, we attached the accelerometers (D2GT; 15mm in diameter, 53mm in length, 18g in air, Little Leonardo, Tokyo) on the mandible of captive harp seals. The experiment showed that frequency filtered signal (Igor Filtering Design Laboratory: IFDL WaveMetrics, Lake Oswego, OR U.S.A.) of acceleration from the mandible is quite distinct at moments of prey ingestion allowing us to use mandible accelerometer for the detection of feeding events of seals in the wild. We attached the same accelerometers equipped with two sensors (surge and heave axes) on the mandible of Weddell seals to detect movements associated with feeding and also swim activities. We successfully obtained feeding data together with stroke and depth data. Here we report the results of the diving behavior and foraging success of Weddell seals in Antarctica.