The novel ribonuclease inhibitor LoRI is a 63 kDa recombinant protein optimized for high-throughput expression in E. coli and purification by metal chelate affinity chromatography (IMAC). The product was obtained by N-terminal fusion of mouse placental RNase inhibitor polypeptide to a thioredoxin module. Advantage of the engineering strategy in terms of protein structure and function was predicted in silico. Under laboratory settings, the yield of purified soluble recombinant product was about 12 mg per 1 L of expression bacterial culture. By RNase inhibition capacity in vitro, the product is comparable or superior to a commercial reference. The kinetic data comply with Lineweaver-Burk model.