The photodecarbonylation of gaseous coumarin was studied using an ArF excimer laser. The triplet state, fluorescence, and cation radical of coumarin were not observed in the transient spectra, The addition of nitrogen effectively quenched the formation of 2,3-benrofuran, indicating that 2,3-benzofuran was derived from the highly vibrationally excited state of coumarin. Transient absorption was proportional to the square of the laser fluence. All of the results showed that the hot coumarin was an intermediate in the two-photon decarbonylation reaction. The decarbonylation reaction of coumarin is the first example of the multiphoton reaction of hot molecules other than hydrocarbons. This new photochemical reaction pathway of coumarin was opened by the hot molecular mechanism.