Flavonoids are well-known for their many therapeutic and pharmaceutical effects. In this study, we tested the antibacterial activity of 11 flavonoids extracted from some medicinal plants by the agar diffusion method. Then, we measured their antioxidant activity using the DPPH (2,2′-diphenyl-1-picrylhydrazyl) radical assay and we also tested their acute toxicity effect on mice. The results showed that apigenin-7-O-glucoside was more active against the Gram-positive bacteria and quercetin was more active against the Gram-negative ones. Also, quercetin and diosmin showed the best antioxidant activity. Quercetin, apigenin-7-O-glucoside, luteolin-7-O-glucoside and luteolin-3′-O-glucuronide gave the best acute toxicity values. It can be concluded that quercetin was the most interesting compound for all the tested activities. Also, we observed that the presence or the absence of substitutions in flavonoids influenced significantly the results obtained, whereas the substitution type had a low impact.