Background: Disease control personnel have an important role in preventing spreading of COVID-19, such as case screening, outbreak investigation, and contact tracing. This study aims to find out their protective behaviors and other associated factors with inappropriate PPE use, as well as the percentage of seropositivity by natural SARS-CoV2 infection in September 2020 during the period without any COVID-19 vaccine. Methods: This is a cross-sectional study of 172 Thai Department of Disease Control personnel, which all had done questionnaires regarding demographic data and protective behavior. The blood test was performed to find out Neutralizing antibody titer (Nab) and Enzyme-Linked Immunosorbent Assay (ELISA). Data were analyzed using descriptive statistics and binary logistic regression was conducted for identifying factors associated with inappropriate Personal Protective Equipment (PPE) use. Results: Of all 172 participants, 38 (22.1%) were Health Care Workers (HCW), 79 (45.9%) were Public Health Personnel (PHP), and 55 (32%) were Non-Health Workers (NHW). Most were female (130; 75.6%). Hand hygiene was the behavior with the highest proportion of being done every time among all participants during work (90.5%), while cleaning high-touch surface and using cashless system were done only a few or sometimes by most participants (55.9% and 56.1%, respectively). Middle age, less experience, and working as Public Health Officers, were associated with appropriate PPE use during work. Participants who had trained for PPE use at least once in the recent year practice inappropriate PPE use less than those who had not been trained, even though there were no significant differences.