In this paper an improvement of the El-Gamal public key cryptosystem is presented. The public key of the El-Gamal system is not changed in this method. But, the sending structure of message and the decryption process are changed. The El-Gamal cryptosystem is not secure under adaptive chosen ciphertext attack. That means El-Gamal cryptosystem can be ciphertext attacked without knowing any key. Therefore changing keys of El-Gamal cryptosystem are not useful. This improvement cryptosystem immunes against CPA and CCA attacks. This cryptosystem is practical and very simple. The importance of this modified cryptosystem is any adversary can’t find the sending message in easily.