Considering importance of N protein for study of viral pathogenesis or development of immunodiagnostic assay we reported effects of several conditions on purity and homogeneity of recombinant SARS-Co V N protein expressed in E. COLI bl21. the SARS-Co V N gene was reverse transcribed and amplified by the reverse transcription-polymerase chain reaction (RT-PCR) technique. The aplicons were cloned into pGEX-6P1 and followed by subcloning of the target gene into pQE-80L. After inserting the recombinant plasmid (pQE80-N) into E. coli the recombinant protein (6 x Histag-N protein fusion) was expressed by inducing the bacterial cells with 0.1-0.5 mM isopropyl-1-thio-D-galactopyranoside (IPTG) for 1-5 h. The protein recombinant were extracted from the bacterial cells by NTT buffer containing 0-20 mM imidazol and followed by Ni-NTA affinity resin purification. The results showed that induction of E. coli BL21 with 0.2mM IPTG for 4 h and followed with lysis of bacterial cell in NTT buffer containing 10mM imidazol were optimal conditions to obtain the pure recombinant SASR-Co V N protein.