We have observed images of Mgr fragment ions produced in ultraviolet laser photodissociation of mass-selected Me+ICH3, ions at 266 nm. Split distribution almost perpendicular to the polarization direction of the photolysis laser was observed in the photofragment image. Potential energy curves of Mg+ICH3, were obtained by theoretical calculations. Among these curves, the excited complex ion dissociated along almost repulsive potentials with several avoided crossings, which was connected to MgI+ + CH3. In the ground state of Me+ICH3, the CH3I was bonded with Mg from the iodine side, and the Mg-I-C bond angle was calculated to be 101.1 degrees. The theoretical results also indicated that the dissociation occurred after the 5(2)A' <- 1(2)A' photoexcitation, where the transition dipole moment was almost parallel to the Mg I bond axis. The Mgr and CH3 fragments dissociated each other parallel to the direction connecting those center-of-masses, which was 67 with respect to the transition dipole moment of 5(2)A' + 1(2)A' photoexcitation. Therefore, the fragment recoil direction was assumed to approach perpendicular tendency against the polarization direction under the fast dissociation process. However, calculated potential energy curves showed a complicated reaction pathway for MgI+ production, including nonadiabatic processes, although the experimental results indicated the fast dissociation reaction.