High total cholesterol (TC) is a robust-documented risk factor for atherosclerosis cardiovascular diseases. Approximately one-fourth (23.5%) of Thai civilians had high TC. However, the information on high TC among the Royal Thai Army (RTA) personnel is limited. The study aimed to identify the trends in serum TC and high TC prevalence among RTA personnel from 2017 to 2022. A serial cross-sectional study from 2017 to 2022 was conducted. A total of 318,353 active-duty RTA personnel aged 35-60 years were included in the study. High TC was defined as fasting TC ≥ 240 mg/dL. A multivariable log-binomial regression analysis was performed to investigate factors associated with high TC. The overall age- and sex-adjusted high TC prevalence was 26.3% in 2017 and dropped to 22.9% in 2020; then, it increased to 26.4% in 2022 (pfor quadratic trend <0.001). Younger-aged RTA personnel have significantly rising trends in sex-adjusted high TC prevalence over 6years. In the south, the age- and sex-adjusted high TC prevalence was 24.4% in 2017 and substantially rose to 33.6% in 2022 (pfor quadratic trend <0.001). Meanwhile, in the northeast, it rose by 3.6% over 6years. High body mass index, high blood pressure, and hyperglycemia were associated with high TC prevalence among this population. High TC was a common essential health issue among RTA personnel. Rising trends in mean serum TC and high TC prevalence from 2017 to 2022 were discovered, especially in younger participants and those residing in the south and northeast.