Facmiles or fax machines are now being used extensively and playa very important role in data communcation. Their prevalent usage in office and military areas demand thet security ber provided to prevent unauthorised access to the transmitted data. The secutiry feature can be designed into a fax machine using a scrambler, which is a device that transposes, inverts or substitute signals. This thesis focusses on the design and development of a scrambler system to proovide a secure facmile communication, particularly for military application. A succesful system has been developed with the implementation of pseudorandom binary sequence (PRBS) signals. With htis system, the input data signal was disquised by encryption process at the transmitter prior tothe modulator. In order to recover the original signal, the demodulated signal was then decrypted at the receiver. The design, construction and test results obtained form each part of the system are adequately described. An overview of the principles and features of a facsimile is also included. Suggestions on ways to improve the system for the actual implementation in the fax machines are given at the end of the thesis.