Introduction: The rise of reemerging pathogens such as DENV and CHIKV presents a major public health threat. With half the global population at risk, Paraguay experiences particularly high infection rates. Despite this, data on the seroprevalence of these viruses in this country is lacking. This study aims to assess the seroprevalence of anti-DENV IgG and anti-CHIKV IgG among blood donors in Paraguay. Material and Methods: Serum samples from 546 blood donors across seven regional departments and Asunción were collected from March to May 2023. Participants filled out a questionnaire and underwent eligibility screening. Serum samples were tested for anti-DENV IgG and anti-CHIKV IgG antibodies using immunoassays. Data were analyzed using IBM SPSS version 23.0. Results: The median (IQR) age of donors was 34 (26-44), and 47.1% were female. Anti-DENV IgG prevalence was 87.7%, ranging from 73.7% to 100% by location, with an age-related association. Donors aged 18 to 25 had a 79.2% seroprevalence, while those over 46 had the highest at 91.5% (p=0.010). Anti-CHIKV IgG prevalence was 37.2%, with men showing a seroprevalence nearly 10% higher than women, but no significant age-related differences were observed. Regional variation in CHIKV seroprevalence was not significant. Conclusions: This study reveals a high seroprevalence of both DENV and CHIKV in Paraguayan blood donors. The high DENV seroprevalence reflects the impact of past outbreaks, while the notable CHIKV prevalence underscores the effects of recent outbreaks. Continuous surveillance, improved diagnostics, and effective vector control measures are essential to mitigate these arboviruses’ impact in Paraguay.