Tellurium (Te) is a trace element widely used in industry. It has been reported that some organotellurium compounds  showed capacity to react with thiols groups from biologically important molecules and to possess  antioxidant activity, specially diphenyl ditelluride.  The aim of this study was to  investigate the potential in vitro toxicity of a new β-organochalcogenyl vinylphosphonate, the diethyl 2- phenyl- 2 tellurophenyl vinylphosphonate, and also to observe a possible antioxidant propertie in comparison with the standard organotellurium compound, the diphenyl ditelluride. Hepatic, renal and cerebral tissues from male wistar rats were used. The organs were removed and homogenized in 10, 7 and 3 volumes of buffer , respectively. After centrifugation the S1 was used for the folowing determinations: delta-aminolevulinate dehydratase (δ- ALA-D) activity (Sassa et al, 1982) and Spontaneous and induced Tiobarbituric acid Reactive Substances (TBARS) formation (Ohkawa et al, 1979). S1 of liver was also used in the DTT oxidation. Diethyl 2- phenyl- 2 tellurophenyl vinylphosphonate was tested at concentrations of 0, 40, 120, 200, 400 and 1200 mM for DTT oxidation and  δ- ALA-D activity and at concentrations of 0, 0.4, 1, 4 and 10 mM for TBARS assay . In the DTT oxidation assay, in the absence of liver S1, diethyl 2-phenyl-2-tellurophenyl vinylphosphonate increased significantly the rate of DTT oxidation after 30 minutes of the start of the reaction (p<0.001). In the presence of liver supernatant, diethyl 2-phenyl-2-tellurophenyl vinylphosphonate did not change the rate of DTT oxidation, probably due to the presence of some tissue factor that has thiol-oxidase activity. Hepatic, renal and cerebral δ- ALA-D activity was significantly inhibited since the concentration of 120 mM, and DTT reversed this inhibtion (p<0.001), indicating that the mechanism of enzyme inhibition involves the oxidation of its essential –SH groups to disulfides. Furthermore, diethyl 2-phenyl-2-tellurophenyl vinylphosphonate decreased the spontaneous TBARS production and showed antioxidat capacity against iron- induced TBARS formation similar to diphenyl ditelluride and at low concentrations. This study confirms that this new organotellurium compound can react with thiols groups and presents antioxidant activity but presents toxic properties in vitro similar to diphenyl ditelluride.