We present the impossible differential cryptanalysis of the block cipher XTEA[7] and TEA[6]. The core of the design principle of these block ciphers is an easy implementation and a simplicity. But this simplicity dose not offer a large diffusion property. Our impossible differential cryptanalysis of reduced-round versions of XTEA and TEA is based on this fact. We will show how to construct a 12-round impossible characteristic of XTEA. We can then derive 128-bit user key of the 14-round XTEA with 2^62.5 chosen plaintexts and 2⁸⁵ encryption times using the 12-round impossible characteristic. In addition, we will show how to construct a 10-round impossible characteristic of TEA. Then we can derive 128-bit user key of the 11-round TEA with 2^52.5 chosen plaintexts and 2⁸⁴ encryption times using the 10-round impossible characteristic.