Lightweight block ciphers, which can be implemented with low cost, are suitable for improving the safety of small devices. PRINCE is a typical lightweight block cipher and suitable for unrolled architecture implementation. In addition, PRINCE can be achieved low latency and embedded in a small area. However, it has been reported that PRINCE with unrolled architecture implementation is vulnerable to power analysis.Regarding countermeasure against power analysis, the threshold implementation and rotating S-boxes masking are popular countermeasures, these require large implementation overhead though. Therefore, this study proposes a low-overhead power analysis countermeasure method for PRINCE with unrolled architecture. Moreover, evaluation experiments using a field-programmable gate array verify the effectiveness of the proposed method. In experiments, the proposed method improved tamper resistance and reduced implementation overhead in comparison with the conventional method. K E Y W O R D S hardware security, lightweight block cipher, power analysis tamper resistance, PRINCE, side-channel attack Electron Comm Jpn. 2020;103:41-53.