Kansai international airport was newly constructed and opened in 1994 at the site of offshore in Osaka bay. This airport was built on the newly reclaimed land. Although similar airport concepts are recently discussed in Japan, yet newly reclaimed land in the deeper sea is very difficult from the points of view of necessity of huge volume of sand for land filling, long period for construction and environmental impacts. On the contrary, concepts of a floating land for the airport are recently discussed again. These concepts were discussed more than a decade ago, even though that was not realized because of no experience of the construction of such huge floating body for the mankind before. After these concepts were proposed, huge floating oil storage bases with million ton capacities were realized in Japan. Therefore, a floating airport should be discussed more and deeper to realize it. The authors wish to show one of the concept designs of floating airport and to discuss the estimates of the environmental forces.