Encoding and decoding of transmitted data through the communication system is considered as an important subject that paid great attention. It is well known that there are many types of error correction codes; some of these types are hamming and extended hamming codes. Hamming code can detect and correct single error while extended hamming code can detect two and correct one only. This work is concerned with the implementation of McEliece cryptosystem by using hamming code and extended hamming code, evaluate the security of this cryptosystem and enhance the performance of it. McEliece cryptosystem is a public key cryptosystem based on algebraic coding theory. The system design and implementation consists of four phases. The first phase is the key generation phase of McEliece cryptosystem using hamming code and extended hamming code. There are three secret keys participate in creating public key (generator matrix, non-singular matrix, and permutation matrix). The second phase is the encryption phase, in this phase the original message is converted to encrypted message. The original message is encrypted by using the public key generated in the first phase, and then adding the error to it. The third phase is the decryption phase. The secret keys are used in this phase to decrypt the encrypted message and to obtain the original one. Also, in decryption process the message is decoded from the errors added to it. The last phase is concerned with evaluating the security of this cryptosystem (McEliece cryptosystem). The evaluation was based on using brute force attack, and the security of this cryptosystem can be measured by its resistance to this type of attack. After applying this attack some weak points have been noticed. To overcome these weak points and to make this cryptosystem more secure, a modification was proposed an implemented. In this phase other cryptosystem parameters have been evaluated, they are: public key size, message expansion and information rate. The security, implementation and the use of this cryptosystem are issues significantly affected by these parameters. All required programs, in this research project have been implemented by using Visual Basic (version 6) programming language working in Window XP operating system platform