Generally, AES is typical encryption algorithm to support the security service of any mobile applications. However, AES cannot encrypt the short sensory data of partial block without data expansion, which is often in the mobile sensing application environments. In this paper, a word-based AES cipher, AESw, is proposed by modifying the AES to make it fit for encrypting the arbitrary message in 32-bit words without data expansion. The proposed AESw would be suitable to encrypt the partial block of a short message, such as using AES3 for the 96-bit Electronic Product Code, and to encrypt the extended block consisting of the last two blocks at one time of long message, instead of encrypting these two blocks separately using the ciphertext stealing method. The proposed AESw could provide an efficient and simple way of preserving the arbitrary word-length of message.