The remarkable wavelengh-dependent photoreactions of 3-methyl-2-(1-naphthyl)-2H-azirine (1) were observed in matrices at 10 K and in solutions at room temperature. Irradiation of 1 with the long-wavelength light (366 nm) exclusively gave the products formed by the cleavage of the C-N bond of the 2H-azirine ring, while the products derived from the C-C bond cleavage were predominantly obtained in the irradiation with the short-wavelength irradiation (> 300 nm).