LED (Light Encryption Device) block cipher, one of lightweight block ciphers, is very compact in hardware. Its encryption process is composed of AES-like rounds. Recently, a scan-based side-channel attack is reported which retrieves the secret information inside the cryptosystem utilizing scan chains, one of design-for-test techniques. In this paper, a scan-based attack method on the LED block cipher using scan signatures is proposed. In our proposed method, we focus on a particular 16-bit position in scanned data obtained from an LED LSI chip and retrieve its secret key using scan signatures. Experimental results show that our proposed method successfully retrieves its 64-bit secret key using 73 plaintexts on average if the scan chain is only connected to the LED block cipher. These experimental results also show the key is successfully retrieved even if the scan chain includes additional some 4000 1-bit registers.