The aim of this work was to evaluate the possible alterations on red blood cell (RBC) membrane induced by a Hypericum perforatum (hiperico) aqueous extract utilizing an optical (OM) and an electronic transmission microscopy technique (TEM) as seen in other publications done the author. Heparinized whole blood from Wistar rat was incubated with hiperico extract, stannous chloride and technetium-99 m, as sodium pertechnetate. Blood sample incubated with 0.9% NaCl was used as control. After that, the blood samples were smeared in slides and stained to be analysed by light field of the OM. Samples (control and treated) of RBC were also prepared to be analysed through TEM. The comparison of the shape of the RBC under OM revealed that the hiperico extract altered the morphology of RBC. The TEM images revealed a not integrity of the membrane with a not continuous electron density and an irregular surface and segmentations in all lengthy of the membrane. In conclusion, the effects observed with the hiperico extract may be due to the products presents in this extract that may alter the morphology of RBC possibly with an action in the membrane structure (lipid bilayers) and possible explain the effects in RBC when it was incubated with hiperico extract and modify the radiopharmaceutical capitation by RBC internal proteins. Moreover, the alterations on the membrane could have been seen with TEM that used very high magnification.