Suvarnabhumi Airport police station was alerted at 8.30am that a foreigner had leapt from the third floor of the terminal to the ground.
The man, identified only as Mikael, 58, from Russia, was rushed to Samitivej Srinakarin Hospital.
Initial police investigation said that the man had taken shelter in the terminal for unknown reasons for a couple of days.
A witness said before that jumping, he had asked for water several times from shops in the airport and looked tense. He suddenly walked to the balcony and jumped.