Being cultured in high cell density, E.coliBL21(DE3) harboring plasmid PET22b-mETIa were induced by IPTG and then recombinant ETIa were highly expressed.Expressed rETIa were above 40% of total bacterial protein.After primary purification through breaking E.coli, dissolving inclusion bodies, refolding,and further purification by two-step chromatographies, rETIa of electrophoretic purtity has been obtained.Inhibitory activity of rETIa against tPA deletion variant (NTA) has been detected and inhibitory constant (K_i) was 8.72×10^－8mol/L.So affinity chromatography column of rETIa-Sepharose 4B was prepared for purification of NTA.After only one-step purification with this column from refolded NTA,13.2-fold puritied NTA with the specific activity of (565.7±71.3) U/μg and above 90% of purity,have been obtained with the recovery rate of 96.2%.