In this paper, we present a new lightweight block cipher named eight-sided fortress(ESF), which is suitable for resource-constrained environments such as sensor networks and low-cost radio rrequency identification(RFID) tags. Meanwhile, we present the specification, design rationale and evaluation results in terms of the hardware implementation. For realizing both efficiency and security in embedded systems, similar to the other lightweight block ciphers, ESF is 64 bits block length and key size is 80 bits. It is inspired from existing block cipher, PRESENT and LBlock. The encryption algorithm of ESF is based on variant Feistel structure with SPN round function, used Feistel network as an overall structure with the purpose of minimizing computational resources. In this paper, we present a new lightweight block cipher named eight-sided fortress (ESF), which is suitable for resource-constrained environments such as sensor networks and low-cost radio frequency identification (RFID) tags. Meanwhile, we present the specification , design rationale and evaluation results in terms of the hardware implementation. For Implementation both efficiency and security in embedded systems, similar to the other lightweight block ciphers, ESF is 64 bits block length and key size is 80 bits. It is inspired from existing block cipher, PRESENT and LBlock. The encryption algorithm of ESF is based on variant Feistel structure with SPN round function, used Feistel network as an overall structure with the purpose of minimizing computational resources.