The flowers of Tagetes patula L., Asteraceae, commonly known as French marigold, are used in folk medicine as an antiseptic, diuretic, blood purifier and insect repellent. This study was conducted to optimize the extraction process through the biomonitoring of flavonoids, using a statistical mixture simplex-centroid design, to evaluate the effect of the solvents water, ethanol and acetone, as well as mixtures of these solvents, assessed by the total flavonoid content. The extracts were tested for dry residue, radical scavenging activity, chromatographic profile, and larvicidal activity. The acetone extract had the highest total flavonoid content, 25.13 ± 1.02% (4.07%); and the best radical scavenging activity, with IC50of 15.74 μg/ml ± 1.09 (6.92%), but with lower dry residue, 6.62 ± 1.33% (20.10%). The water extracts showed higher levels of dry residue, but lower total flavonoid content and radical scavenging activity than the acetone extract. The positive correlation between the total flavonoid content and radical scavenging activity of the extracts showed that flavonoids contribute significantly to the antioxidant capacity. The statistical mixture design allowed us to optimize the extraction of flavonoids from flowers of T. patula, with acetone as the best extraction solvent. Preliminary studies on the biological activity of the optimized extracts demonstrated a larvicidal effect of the acetone extract on Aedes aegyptimosquitoes.