Executive functions (EFs) are essential for daily living activities but decline with age. Convenient assessment and timely intervention have particular significance for older adults. However, the traditional laboratory tasks of EFs are typically monotonous and inconvenient. The current study aimed to develop an interesting and convenient supplementary tool to assess EFs for older adults. According to the theory of EFs, we developed a serious game, FISHERMAN, to assess EFs. The game includes three subgames, Cautious Fisherman, Agile Fisherman, and Wise Fisherman, targeting core components of inhibition, shifting, and working memory, respectively. The current study aims to verify the reliability and validity of the game. One hundred and eight healthy older adults participated in this study and were tested through the FISHERMAN game and a battery of cognitive tests. The results show that the FISHERMAN game has high internal consistency reliability and good construct validity as well as criterion-related validity, suggesting that the game design is valid and can be used in EFs assessment for older adults. Future studies are warranted to establish the norm of the FISHERMAN game in older adults and investigate whether the FISHERMAN game can be generalized to other populations.