A method and apparatus for a fast access considering service assistant information in a wireless communication system is provided. A wireless device selects a new cell. The wireless device performs a Random Access (RA) procedure to the new cell. The wireless device performs a cell reselection procedure based on a mobility information. The RA procedure includes (1) selecting a special RA preamble for service assistance information related to an intended slice, (2) transmitting, to the new cell, a RA message including the service assistance information; and (3) receiving, from the new cell, a response message including the mobility information.