Variations in the degree of deterioration of a concrete structure are caused by variations in concrete quality and environmental impacts. Moreover, variations in concrete quality are also influenced by the segregation of fresh concrete due to vibration and bleeding. Considering this background, the degree of segregation of fresh concrete and its factors caused by vibration were experimentally investigated. As a result, it is found that the gravel settled due to the vibration while compacting the fresh concrete, whereas the cement paste rose up. Moreover, the longer the vibration time, the larger the amounts of risen cement paste and settled gravel. In addition, it is concluded that the mortar apparent viscosity and the inter-gravel average distance influenced the segregation of fresh concrete due to vibration.