In Tunisia, the measles vaccine is included in the national-immunization-programme. An outbreak of measles occured with 3896 notified cases and 39 deaths in 2019. We conducted this study to estimate measles IgG-antibodies seroprevalence before the occurrence of 2019-outbreak. We conducted a national seroprevalence survey of measles immunity using blood samples serotheque collected during the 2014-2015 National Viral Hepatitis cross-sectional survey. Written informed consent for using the sera for further analysis was obtained from participants (parents for minors). A subsample of 3500 individuals was included based on expected seroprevalence of 85%, a precision of 0.2% and 95%CI. ELISA was used to detect IgG antibodies against measles. Participants with serum positive for measles antibody were considered protected or immune to measles disease. From 3454 serum samples tested , 3279 were positive for measles IgG antibodies, representing a seroprevalence of 94.9% (95%CI: 94.3%-95.6%). Seroprevalence was significantly lower in rural area(p<0.001). The prevalence of measles IgG antibodies was different by age(p<0.001). The seroprevalence among children aged 0-5 years was 94.7%. It was 96% for both 5-10- and 10–15-year-old populations. However, it declined significantly among 20-30 years population, 1982-1997 birth cohort, with a seroprevalence of 83.2% (95%CI: 79.7%-86.1%). Among 40-50, 50-60 and >60-year-old populations, seroprevalences were to 98.1%, 99.2%, and 98.6% respectively. In this context, during 2021, the Tunisian government, provided and recommended getting a booster dose targeting adults born between 1982-1997(20-30 years), and advancing the first dose for children from 12 to 9 months, in order to ensure a sufficient immunization rate. This study, a pre-epidemic measles seroprevalence survey, showed that seroprevalence among vaccinated population aged 20-30 years in Tunisia was low. To prevent future outbreaks, a nationwide-vaccination-campaign was implemented in 2021, aiming to boost immunity against measles. It was delayed for 2022, as a consequence of the Covid-19 pandemic.