AbstractThis study aims at describing the evolution of Spanish population preventive practices during the COVID-19 pandemic of the between January and June 2021, and differences by age group. Data was drawn from the COSMO-Spain online survey, rounds (R) 4, 5 and 6. Multiple linear regression models with preventive practices as dependent variable were performed. Preventive practices (p = 0.001) and concern about coronavirus (p = 0.003) decreased throughout the three rounds, knowledge decreased from R4 to R6 (p = 0.002) and health literacy had a higher value in R6 (p < 0.001). Older the age was associated with higher the frequency of preventive practices, and levels of health literacy and concern about coronavirus (p < 0.001). The regression model showed that, in the 18–29 year group, a greater frequency of preventive practices was associated with being female (β = 0.20; p < 0.001), greater concern about coronavirus (β = 0.16; p < 0.018) and frequency of information seeking (β = 0.24; p < 0.001). For 61 years old and older, a higher frequency of preventive practices was associated with greater concern about coronavirus (β = 0.21; p < 0.002) and lower pandemic fatigue (β = − 0.13; p < 0.037). These findings point to the need for effective public health interventions tailored to the characteristics of age population groups.