The guava plant, Psidium guajava L., serves as proof of the abundant donations of nature, providing a delicious guava fruit; this plant is rich in groups of medicinal and nutritional benefits. Guava belonging to the Myrtaceae family, many previous studies reported many phytochemical constituents in its leaves that have many pharmacological activities and medicinal properties; this study focuses on the isolation, structural elucidation and calculation concentration of flavonoids, assessment of the cytotoxic activityof hyperin from Psidium guajava leaves newly cultivated in Iraq. The isolation process involved the use of thin-layer chromatography (TLC) and preparative high-performance liquid chromatography (PHPLC) and structural elucidation involved NMR (nuclear magnetic resonance spectroscopy) and FTIR (Fourier transform infrared spectrometer) for detailed structural insights into 2 isolated flavonoids. The isolation techniques proved effective in obtaining pure samples of hyperin and naringenin from the ethyl acetate and n.butanol fractions and structural elucidation techniques gives a good explanation for 2 isolated flavonoids. Evaluate cytotoxic activity of hyperin flavonoid against prostate cancer cell line (PC-3), human breast cancer cell line (MCF-7) and normal dermal fibroblast neonatal (HdFn), hyperin flavonoid exhibited a decrease in cell viability (%) with IC50 58.9 ?g /mL against the prostate cancer cell and IC50 90.58 ?g /mL against human breast cancer and noncytotoxic to HDFn, with an IC50 value substantially surpassing concentrations of 100 ?g/mL. These analytical approaches provided a comprehensive understanding of the chemical composition of the isolated flavonoids and interpreted that guava has cytotoxic activity against some cancers, depending on a concentration-dependent mode.