Expression of giant catfish growth hormone (gcGH) gene under the control of the lambda Pr promoter was comparatively low in Escherichia coli. mRNA secondary structure analysis predicted that there are new two hairpin loops: one at the Shine Dalgarno (SD) sequence region with ?G = 7.9 kcal/mol, the other at the initiation codon region with ?G = 4.2 kcal/mol. The effect of the mRNA secondary structures on the expression level of gcGH gene in E. coli was investigated. Several site specific mutations were introduced into stem loops at the Shine Dalgarno (SD) sequence region and the initiation codon region to disrupt the secondary structures. Completely destabilizing the stem loop at the SD sequence region while maintaining that at the initiation codon region, or vice versa, increased gcGH gene expression level fifty five and fifty folds, respectively. Complete destabilization of the two stem loops hence creating a new stem loop increased the gcGH expression one hundred and five fold.