A novel photochemical ring-contraction reaction of 5-unsubstituted 3, 1-benzoxazepines and their 5-halogeno or carboxyl derivatives to yield 3-formylindoles in an aprotic solvent is reported. This ring contraction was successfully extended to oxazepines having an alkoxycarbonyl function at the 5-position to give the indoles having this function at the 3-position. Though most of the oxazepines underwent the ring-contraction reaction only on irradiation at 254 nm, 5-carboxy derivatives or their esters afforded the ring-contraction products even at ≥ 300 nm. The intermediacy of 3H-indole species in these photochemical ring-contraction reactions was demonstrated by the isolation of methyl 3-acetyl-2-phenyl-3H-indole-3-carboxylate during the photolysis of methyl 4-methyl-2-phenyl-3, 1-benzoxazepine-5-carboxylate. It was found that this 3H-indole afforded methyl 6-and 4-acetyl-2-phenyl-indole-3-carboxylates upon further irradiation. The mechanism of this acetyl migration is discussed based on the result of the photochemical acetyl migration of methyl 1-acetyl-2-phenylindole-3-carboxylate.