A new graft cactus (Gymnocalycium mihanovichii) cultivar, 'Simhong' was developed from a cross between graft cactus breeding line 'Keumhong', a cultivar revealing a red colored globe with yellow colored tubercles, and a dark red line '9502052' and consecutive line selection at the National Horticultural Research Institute, Rural Development Administration in 2005. It was developed with the aim to breed a dark red cultivar. Its characteristic evaluation was conducted three times during 2003 to 2005. The color of both body and tubercle was dark red. The shape of the globe was flattened round and it had 8 to 10 deep ribs. The spine was medium sized, straight and dark brown. Its growth was faster than the comparison cultivar, 'Jinhong'. Propagation capability was excellent, setting 12 tubercles per globe. Characteristics of the cultivar could be maintained by vegetative propagation. Strong sun light and virus infection should be avoided.