Two cruises (offered by R/V Fishery Researcher I) were conducted in July 2000 and June 2001 in order to examine the geographical distribution pattern of tuna larvae in the central-western Pacific Ocean. At each station, IKMT and CTD were deployed to collect ichthy-plankton samples and to measure relevant oceanographic factors. Totals of 33 and 34 stations were surveyed in 2000 and 2001, respectively. The latitude reached to 10°N in the south, while the longitude reached to 141°E in the east. Tuna larvae were identified by examining patterns of melanophore which appeared on the body. A total of 90 tuna larvae were obtained, including 11 bluefin tuna (Thunnus orientalis), 20 bigeye tuna (T. obesus), 54 yellowfin tuna (T. albacores), and 5 albacore (T. alalunga). No significant differences in the mean standard lengths for the four tuna species were found between the samples from 2000 and 2001. The standard lengths of bluefin tuna, bigeye tuna, yellowfin tuna, and albacore larva ranged from 3.4 ~ 8.1 mm, 2.9 ~ 9.8 mm, 3.8 ~ 7.8 mm, and 4.1 ~ 8.1 mm, respectively. The spawning period for tunas was considered from June to July. Furthermore, the spawning grounds of tunas were also suggested to be adjacent to the eastern waters off Taiwan.