AIM: To construct a high-level expression system of recombinant human neuronal nitric oxide synthase (hnNOS) full-length enzyme in Escherichia coli. METHODS: The coding sequence of hnNOS full-length was firstly amplified by PCR, and then ligated into the expression vector pCWori+. The recombinant plasmid was transformed into Escherichia coli BL21 for high-level expression. After having been checked with Western blot, the enzyme was used for large-scale culture and purification. Finally, the property of the enzyme was determined by spectrophotometric method. RESULTS: The constructed expression system could give a yielding of 3 mg/L initial culture. CONCLUSION: The expression system constructed is fully sufficient to express the active human neuronal nitric oxide synthase.