β-nicotinamide mononucleotide (NMN) has several beneficial effects. However, it remains unclear whether it has sleep-protective effects in middle-aged and old adults. Fifty-eight volunteers underwent a 12-week treatment period. They were randomly divided into NMN and control groups to observe and compare NMN’s effect on insomnia in middle-aged and old adults. Its efficacy was evaluated using the Pittsburgh Sleep Quality Index (PSQI) and smart bands (Huawei Band 6) sleep data. Each group’s PSQI total and item scores decreased before and after treatment. Significant differences were observed in the total PSQI score, sleep quality, sleep latency, and daytime dysfunction(P < 0.05). The total effectiveness rate was significantly higher in the NMN group (65.52%) than in the control group (27.59%; P < 0.05). Sleep data recorded by their smart bands indicated better sleep quality in the NMN group. These findings show that NMN improves sleep quality in middle-aged and old adults. (Am J Transl Med 2022. 6(4):167-176).