This cross-sectional study was conducted in government tertiary hospitals across fourteen states in Malaysia between August and November 2017. This study aimed to evaluate the seroprevalence of diphtheria among the Malaysian population. The sample consists of 3317 individuals aged 2 to 60 years attending various hospital clinics, including outpatient, pediatric, medical, obstetrics, gynecology, orthopedics, daycare, and the blood bank. The sample size was proportionally distributed based on state population size, with hospitals selected accordingly. Participants were excluded if they had a fever, severe illness, psychiatric disorders, or immunocompromised conditions. Enzyme-linked immunosorbent assay (ELISA) was used to measure the level of IgG antibody against the toxoid of C. diphtheriae in the blood samples of respondents. One article has been published from this study Yusoff AF et.al. Seroprevalence of diphtheria toxoid IgG antibodies in the Malaysian population. BMC Infect Dis. 2021 Jun 16;21(1):581. doi: 10.1186/s12879-021-06285-3.