Gas-phase complexes Mg+-[HCON(CH3)(2)](1,2) are mass-selected and studied by ultraviolet laser photodissociation in a time-of-flight mass spectrometer. Beside the dominant evaporation photofragments, some photoreaction products have also been detected from both complexes. Quantum mechanics calculations and deuterium-substitution experiments are employed to facilitate the structural, energetic, and mechanistic analysis of the photoreactions. For the most stable structures of the complexes, Mg+ is linked to the carbonyl oxygen atoms and situated trans to the -N(CH3)(2) groups. Starting from these complex structures, photoproducts are generated through (1) H abstraction next to the carbonyl group by the photoexcited Mg+* (to form (CH3)(2)NCO+) and/or (2) the subsequent CO loss (to form CH3NH+=CH2). For Mg+-[HCON(CH3)(2)](2), the further solvation tends to hold back the photoreactions because of the even more facile evaporation channels.