The users of mobile based on Android were increasing every day. Mobile phone users send and receive a simple text message by using Short Message Service (SMS). When a user sends any confidential data through the message it is very difficult to protect it. SMS does not provide a secure medium. Information about every aspect of our lives needs to be kept secure from attackers and transfer safely over an insecure channel. Cryptography provides security services that enhance the security of data processing systems and transfers of information. Encryption, hiding or covering data provides data confidentiality. Asymmetric key cryptography algorithm RSA is used for encryption and decryption of the message. The user can obtain security of text message using RSA. In this system, the RSA algorithm is used for providing a secure medium on the mobile platform.