Exclusion of native ant species by invasive ones is one of the most intense and widely known negative impacts by invasive species. Anoplolepis gracilipes (yello crazy ant: YCA) and Pheidole megacephala (BHA: bigheaded ant) are listed as the 100 worst invasive alien species in the world because of their negative impacts to ecosystems. These two species have also been recognized as invasive species in Okinawa main island. However, there is no data to support that they have excluded native ant species in Japan. In order to verify their impacts on native ant fauna in Okinawa, we investigated ant fauna by pitfall traps and by soil and litter samplings. Abundance of each of all ant species and species richness are compared between infested and non-infested areas for YCA and BHA. As a result, strong exclusion of native ant species by BHA was observed though its abundance was much lower than previous studies. However, in our survey, BHA disappeared from in five out of seven previously reported distributional areas. This suggests that its colony does not persist for long though reasons are not clear. Exclusiveness of YCA to native ant species was not detected in this research. Thus, in Okinawa, both BHA and YCA would not be as a great threat to native ant fauna as reported in abroad.