A visible-light-induced reaction of an O-3-trimethyl-amine (TMA) complex isolated in low-temperature noble-gas matrices is investigated by infrared (IR) and visible absorption spectroscopies using the DFT calculation. The complex isolated in a Ne matrix yields trimethylamine-N-oxide (TMAO) upon irradiation (lambda >= 800 nm) by dissociation of O-3. When the wavelength of radiation is changed to lambda = 455 nm, two stable conformers of dimethylaminomethanol (DMAM) are recognized besides TMAO. In an Ar matrix, DMAM and not TMAO is mainly produced upon lambda = 455 nm irradiation. The photoreaction mechanism of the O-3-TMA complex with a single collision reaction between O(P-3) and TMA in the gas phase to produce OH and CH2N(CH3)(2) radicals is discussed.