Mild cognitive impairment (MCI), an intermediate condition between healthy cognitive changes due to aging and dementia, is a risk factor for dementia. Cheonwangbosim-dan (CWBSD) is a traditional herbal medicine widely used to improve mental and physical illness in East Asia. We aimed to investigate the safety and efficacy of CWBSD in the treatment of MCI. This clinical trial adopted a double-blind, single-center, parallel-arm, prospective, randomized controlled pilot study design with a full analysis set. Forty-eight participants with MCI were randomized to the control or CWBSD groups. The participants were administered either placebo or CWBSD once daily (at a dose of 3 g) for twenty-four weeks. The primary outcome measure was a change in the Korean version of the Montreal Cognitive Assessment Scale (MoCA-K). The secondary outcome measures included memory, quality of life, depression, and level of activity in daily living. Safety measures were conducted by comparing the occurrence of adverse events and changes in blood chemistry parameters, pulse rate, and blood pressure between the two groups. After 24 weeks of treatment, no significant differences in the changes in the total MoCA-K scores were detected between the two groups. Changes in secondary outcomes were not significantly different between the two groups. In the safety evaluation, there was no significant difference between the two groups with regard to the occurrence of adverse events and changes in blood chemistry parameters, blood pressure, and pulse rate. We demonstrated that CWBSD treatment may be safe and does not significantly improve cognitive function, quality of life, daily activities, or depression in individuals with MCI. Further studies are necessary to validate the efficacy and safety of CWBSD in the treatment of MCI. Trial registration Clinical Research Information Service KCT0006787.