A direct micro determination of glutathione peroxidase (GSH-PX) activity with spectrophotometry was developed. Conditions of the assay were studied in detail. 10μl blood sample was diluted with distilled water and treated with 10% TCA to remove protein.There was a good linearity between DTNB product and concentration of GSH after 3 minutes enzymatic reaction at the temperature of 37℃ in PH 6.5 solution. The method had higher sensitivity, better reproducibility. It may became useful tool for analyzing GSH-PX in scientific research and clinical work.