Based on seven bottom trawl surveys conducted in the central and southern Yellow Sea,which covered the range of 120°-124°E,33°-37.5°N,in seven months from January 2006 to July 2009,total of 3 005 stomach samples of seasnail Liparis tanakae with body length of 18-525 mm were collected.Stomach content analysis,cluster analysis and trophic level were used to study the feeding habits and their ontogenetic variation and monthly variation.The results showed that seasnail is important fish species in food web and plays an important role in the marine ecosystems of the Yellow Sea.Seasnail fed on more than 60 prey species.Crangon affinis was the dominant prey item of seasnail,and Enedrias fangi became the dominant prey item instead of anchovy Engraulis japonicus. The feeding habits of seasnail had significant monthly and ontogenetic variations.Seasnail mainly fed on benthon at less than 50 mm body length; on zooplankton,benthon and demersal shrimps at 51-100 mm body length; When it mainly fed on demersal shrimps at 101-350 mm body length,the frequency of fish in the food increased gradually with increasing fish size,whereas the frequency of demersal shrimps decreased; It mainly fed on demersal shrimps and fish at greater than 350 mm body length.Therefore,there were three shifts in feeding habits in the fish at about 50 mm,100 mm and 350 mm body length,respectively.Seasnail at different body lengths belonged to different functional groups in the Yellow Sea ecosystem.Seasnail with less than 50 mm body length belonged to benthivores functional group,fish with 51-100 mm body length belonged to generalist predators functional group,fish with 101-350 mm body length belonged to shrimp predators functional group,and fish with greater than 350 mm belonged to shrimp/fish predators functional group.The food composition of seasnail varied monthly.Cluster analysis revealed that feeding habits in seven months could be divided into four groups.The body length was the main factors that cause monthly variation in feeding habits of seasnail.Seasnail was one kinds of fish with higher feeding activity in the Yellow Sea,but the feeding activity,as indicated by the percentage of empty stomachs(PES) and mean stomach fullness index(MSFI),varied significantly among different classes of sizes and different months.The PES and MSFI each had highest value at 101-150 mm and 51-100 mm size classes,respectively,then all decreased with increasing fish size.So,seasnail with small size obtained higher feeding activity by higher food consumption,but fish with larger size obtained higher feeding activity by higher feeding opportunity.By integration of the PES and MSFI in each month,seasnail had two feeding peaks in August and January in a year.