This thesis presents a design and development of the Access Control System by magnetic cards .The system compose of two units , server module and terminal module. The terminal module and the server module connect by RS485 help for communication .Server is a centralized host that hooks maximum up to 32 terminals via RS485 .Each terminal has function read magnatic cards information and time of user . The protocal use as the rule of data communication in this specific system is based on the HDLC. MCS51 is selected to be the processor units of both server and terminal module. The system was distributed using encoders to detect the angle of the pendulum, and the system is controlled by computer.