Psidium guajava L. has extensive use in folk medicine. The aim of this study was to quantify the levels of phenolic, flavonoids, antioxidant activity, leathality assay and antibacterial and antitumoral activities of the extract of P. guajava. In the dry guava extract there were high levels of phenolics (766.08 ± 14.52 mg/g), flavonoids (118.90 ± 5.47 mg/g) and antioxidant activity (87.65%). The LD50 was 185.15 µg/ml. The MIC value was 250 µg/ml for Streptococcus mutans, Streptococcus mitis and Streptococcus oralis. IC50 of the extract tested in the HeLa, RKO and Wi cell lines was 15.6 ± 0.8 µg/ml, 21.2 ± 1.1 µg/ml and 68.9 ± 1.5 µg/ml, respectively. The results of all analyses allow us to conclude that the dry extract of guava leaves has promising activity to be applied topically in the oral cavity or in the development of antitumor formulation or even be used as a functional food.