The present invention relates to Random Access Channel (RACH) access apparatus for mobile satellite communication system and method therefor. The method for accessing random access channel (RACH) on satellite system, random access channel (RACH) carrying message data from a plurality of mobile stations to the satellite system, the method includes the steps of: receiving preamble and the message data, the message data successively transmitted with the preamble from the plurality of mobile stations; and transmitting acquisition response signal corresponding to the preamble or the message data to the plurality of mobile stations. Accordingly, success of packet reception of satellite system is improved and transmission delay is reduced.