Human beings have been widely used natural products as medicines. However, there are many reports about their undesirable toxicological effects. Chitosan is a kind of polysaccharide derived from the chitin (copolymer of "-(164)-D-glucosamine and $-(164)-N-acetil-D-glucosamine) that it is found in abundance in the nature, mainly crustaceans. It Had to the basic character, attributed to the presence of the grouping amine in the repeated units, and to its biodegradability, these two polymers come sufficiently interesting in scientists and technologists, who have discovered diverse applications, especially in the biomedical area. It is concerned that many natural remedies may contain potentially toxic ingredients and contaminants such as heavy metals. Red Blood Cells (RBC) and plasma proteins labeled with technetium-99 m (99 mTc) have several clinical applications and it has been reported that some natural products are capable of reducing the efficiency of this radiolabeling. The aim of this study was to assess the effect of a chitosan extract on the labeling of blood elements with 99 mTc. In the preparation of the extracts it was used 310mg of chitosan diluted in 10mL of saline solution (NaCl 0.9%). Samples (0.5 mL) of blood from Wistar rats were incubated with 0.1 mL of the extracts during 1 hour. After that, the samples were incubated with stannous chloride (SnCl ) and 99 mTc. The blood was centrifuged and Plasma (P) and RBC were isolated. P and RBC were also precipitated with Trichloroacetic acid (TCA) 5% and Soluble (S) and Insoluble (I) Fraction (F) was determined. The results have shown that the extract has not altered the radiolabeling . It was described that some extracts as Fucus vesiculosus, Paullinia cupana, Mentha crispa L were able to alter the radiolabeling of blood elements. In the light of the results obtained we suggest that the referred extract has an antioxidant properties.