Based on the data collected by National Tuna Scientific Observer's Program in the west-central Indian Ocean during December 2003 to June 2004 and September to December 2005, the paper preliminarily analyzed diet composition and its variation over months and fork length, feeding intensity and food items'niche breadth of yellowfin tuna Thunnus albacares by using the two-way contingency table test and one-way Analysis of Variance. The results indicated that diet compositions of T. albacares included Alepisaurus, Scomber, Nautilus, Katsuwonus pelamis, Sardinaa, Octopus, Trachurus, shrimp, crab, squid and other fishes, with squid, Scomber and crab as the main diet item according to the percentage of occurrence. Over 70% of ingestion rates for all fork length classes of T. albacares sampled were found during most months of a year. Food item replacement rates of T. albacares were below 50% year round excluding February and June and below 40% for 106-155 cm fork length class. Significant difference in feeding intensity of T. albacares appeared between months, but non-significant difference occurred among the fork length classes. Significant difference also indicated between monthly stomach fullness indexes. Significant changes in diet compositions of T. albacares were found among both months and fork length classes. Squid, Scomber, and Mautilus were fed as the main food by all fork length classes T. albacares. Monthly Shannon-Weiner diversity index of diet composition of T. albacares varied greatly and significant T. albacares maintained at the level of 0.80-1.00 and asignificant difference between the indexes appeared. Big variation of Shannon-Weiner diversity index of diet composition of T. albacares occurred to all fork length classes. Significant differences can be found in Shannon-Weiner diversity index and Pielou's evenness index of diet composition of T. albacares among both months and fork length classes. It is the first time for our Chinese scientists to attempt the feeding habits analysis of T. albacares in the western and central Indian Ocean due to the limitation of sample size, sampling period (less than one year) and lack of experience in identifying food items, the authors only focused on the feeding habits analysis of T. albacares in the western and central Indian Ocean in preliminary way, further research should be carried out on the position of T. albacares in the marine ecosystem and the food relations between T. albacares and other tuna species and pelagic species.