This paper aims at contemplating the semantic network of horses in Mongolian nomadic culture through the configuration of horses described in Beijing edition Geser. Geser is a heroic narrative story which arose from 10th century Tibet and became spread throughout the East Asia. Depending on the regional variation, the story is interpreted as a myth, or understood as a historically reflected heroic epic or as a pure literary piece. Thus, it is an important source to clarify the East Asian world-view. A horse in Mongolian nomadic culture has a meaning of something more than a domestic animal. No nomadic culture can be founded without horses. It is because horses make cattle pastures in wide meadow and long-distance plundering wars possible. In Geser, horses are described as transportations both in daily lives and in wars, as spoils of wars, as objects of sacrifice, and as forecasting methods, and such descriptions represent the nomadic culture. The configuration of ``Bilig-un keger morin`` clearly shows the status of horses in the nomadic culture. Bilig-un keger morin, that is a sacred horse, is described not as a mere horse but as an assistant and companion of Geser Khan. It can be said that the heroic epic of Geser Khan cannot be formed without Bilig-un keger morin. It represents the fact that nothing can be done without horses in nomadic cultural region. Horses appearing in Geser are described as domestic animals, as helpers, and as beings with divinity. Such configurations of horses show the characters and the status of horses in the nomadic culture. In other words, it confirms that the strongest key-word to understand the nomadic culture is a horse.