This 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.