The study includes the preparation of gold nanoparticles-GNPs by chemical synthesis and loading of isolated flavonoids from Cymbopogon citratus on GNPs. For GNPs and flavonoids-loaded-GNPs characterization, transmission electron microscopy–TEM, ultraviolet-visible(UV) spectroscopy and Fourier-transform infrared spectroscopy are employed.
            Twenty-five adult male rabbits were used, divided into five main groups (5 rabbits in each group): Negative control group(C- ) orally treated with drinking water only, Positive control(C+) orally treated with parasite cysts (4×10³cysts /ml) to induce Giardiasis, the first group(G1): treated with 30mg/kg/day of metronidazole after inducing Giardiasis, while the second group(G2): treated with100mg/Kg/day of GNPs after inducing Giardiasis, and third group (G3): treated with 50 mg/Kg/day of flavonoids-loaded GNPs after inducing Giardiasis.
            The result of TEM analysis showed that the mean size of the isolated flavonoids was 433 nm, irregularly spherical, and the mean of GNPs was 14.1 nm and the shape of the particles was spherical, While the mean size of flavonoid-loaded- GNPs was 17 nm, and the particle shape was spherical.The treatment response showed that the treatment response with metronidazole(in G1) was lower than the treatment with the GNPs(in G2) and flavonoids-loaded GNPs (in G3). The C+ indicates an increase in the cysts number in the 1^st,2^nd and 3^rd  days after inducing infection with the parasite, and then the number of cysts gradually decreased on the 4th day after the infection to the lowest value on the 10th day. The treatment response for GNPs(G2) was on the 3^rd day, while in G3 the treatment response appeared on the second day.   From the results of this study, we can conclude that gold nanoparticles and flavonoids-loaded-GNPs showed higher efficiency in the treatment of the infection with Giardia lamblia than metronidazole.