Abstract: The feasibility of using lactose as an inducer to substitute the common inducer IPTG ( isopropyl-β-D-thiogalactopyranoside) to induce the expression of D-tagatose 3-epimerase in E.coli BL21 ( DE3 ) was investigated.The effects of the main factors of induction such as the optimal time of induction, the concentration of the inducer, the duration and temperature of induction were analyzed.The result showed that the optimal condition was to add 5g/L ( final concentration) lactose at the mid-log-phase of cell growth ( OD600 = 1.0) and incubate at 20℃ for 7h.Under this condition, the enzyme activity, the soluble recombinant protein expression and final biomass induced by lactose was 82.7% , 99.5% , and 30.5% higher than induced by IPTG, respectively.The results indicated that lactose could be used as a promising inducer in the production of recombined D-tagatose 3-epimerase.