Isolated molecules of Gd@C-82 metallofullerenes were directly observed by high-resolution electron microscopy. The sample was prepared by vacuum deposition on MgO single crystalline (001) films in a sample-transfer chamber attached to an electron microscope for observation under anaerobic conditions. The image contrast corresponding to one Gd@C-82 molecule was detected as an elliptic ring with some contrast due to a Gd atom inside. The present study shows the clear possibility of studying various types of mono-molecular level fullerenes by using high-resolution electron microscopy.