A fish aggregating device (FAD) called a payao is conventionally installed to catchpelagic species in the Philippines. The waters around the Philippines are importantregions for yellowfin tuna stocks because they include spawning grounds and nurseries. Tounderstand the schooling behavior of juvenile yellowfin tuna Thunnus albacares around a payao, 13 juveniles (20.5−24.0 cm fork length) double tagged withultrasonic transmitters (V7-2L-R256; Vemco Ltd.) and data loggers (DST-micro; Star-OddiLtd.) were released around a payao. A self-recording receiver (VR2-DEL; Vemco Ltd.) wasattached on the mooring rope of the payao to follow the horizontal movements and dataloggers recorded the vertical movements of tagged juveniles. Nine juveniles wererecaptured simultaneously by ring net at the same payao after 4-7 days. One juvenile wasrecaptured by hand line at another payao 12 km away from the tagging site after 6 days.Recaptured juveniles showed a diurnal schooling pattern suggesting different school shapeand foraging strategy between daytime and nighttime. Juveniles showed a diurnal horizontalmoving pattern, concentrated near the payao during daytime, while they were distributedaround the payao at nighttime. The fluctuations of swimming depth were synchronized amongfish. Juveniles also showed a diurnal vertical movement pattern in surface mixed layer.They concentrated in a shallow and narrow range (11.2±8.2 m, mean ± SD) at nighttime,while they were distributed to a deep and wide range (20.0 ± 11.8 m) during daytime. Themaximum vertical neighbor distance indicated the vertical thickness of the school andshowed a peak around noon. Higher vertical movement speed during daytime indicatedvertical foraging in a water column, while at nighttime the juveniles might foragehorizontally following the diurnal migration patterns of prey in the surface layer.