Organophosphate pesticides have their inhibitory action on the chorinesterase. It is likely that application of organophosphate pesticides invoke retardation in activity as well as death of arthropods. This study is aimed to find changes in foraging activity of ants due to application of fenitrothion, one of most widely used organophosphate pesticides. Foraging activity (FA) of ants was observed by using bait cards at pesticide sprayed pine stand and unsprayed stand before and after aerial application of fenitrothion in 2003 and 2004. FA of Paratrechina flavipes which was too abundant to be statistically compared, significantly decreased from 2 hours to 10 days after application of the pesticide but recovered at 16 day in 2003 and partially recovered at 18 day and completely at 31 day in 2004. FA of other ant species also significantly decreased during the retardation period of FA of P. flavipes. Ratio of ants feeding on baits significantly decreased during the retardation period of FA. However, decrease of interspecific inhibition on feeding action, which was expected for negligence on other ants caused by the chorinesterase inhibition was not observed.