A series of 2-(3,5-dimethylpyrazol-1-yl)ethylseleno derivatives has been synthesized. The glutathione peroxidase like catalytic activity of these compounds has been studied in a model system, in which reduction of hydrogen peroxide with dithiothreitol (DTTred), in the presence of an organoselenium compound was investigated by 1H NMR spectroscopy. All these compounds exhibit GPx like catalytic activities and the catalytic reaction proceeds through a selenoxide intermediate, identified by 77Se{1H} NMR spectroscopy.