Granzyme A is a member of the granzyme family of the serine proteases found specifically in the cytotoxic granules of cytotoxic T?lymphocytes (CTL) and natural killer (NK) cells. Granzyme A is the most abundant protease in CTL and NK cells. It induces caspaseindependent cell death when introduced into target cells by perforin (1). Mouse granzyme A is synthesized as a precursor (262?residues) with a signal peptide (residues 126), a propeptide (residues 27-28) and a mature chain (residues 29-262). The purified recombinant mouse Granzyme A consists of residues 29 to 262 which activity was measured by its ability to cleaves a thioester substrate Z-Lys-SBzl?HCl. The reaction was performed in 0.05 M Tris, 0.15 M NaCl, 0.01% Triton X-100, pH 8.0 (Assay Buffer), initiated by addition 50 μL of various concentrations of GZMA (dilute by Assay Buffer) to 50 μL of 1.2 mM Substrate and DTNB mixture. The final well serves as a negative control with no GZMA, replace with 50μL assay buffer. Incubated at 25℃ for 5min, then read at a wavelength of 405 nm. The specific activity of recombinant mouse Granzyme A is 6214 pmol/min/μg.