In this study we tried to construct a more efficient tetracycline-inducible gene expression system by replacing previous key elements with more advance ones. At the beginning, we substituted PGK (phophoglycerate kinase) promoter for CMV (cytomegalovirus) promoter to control "$rtTA2^sM2$" which has been known for high induction efficiency in response to tetracycline. With this modification, expression of the EGFP marker gene under the induction condition was significantly increased. Next, we replaced "TRE" fragment with a modified version named "TRE-tighf" which has been reported to have higher affinity and specificity to the transactivator by minor base change of the "TRE" DNA fragment sequence. Use of "TRE-tighf" instead of "TRE" resulted in more than 10 fold increment in terms of induction efficiency and significant decrement of background expression in non-inducible condition. By combining PGK promoter and "TRE-tight" fragment, we could upgrade previous tetracycline-inducible system to show more stringent turn on/off gene switch ability and stronger expression of the gene of our interest. Use of this newly developed system must be very helpful to the studies of gene expression, especially to the transgenic animal study in which non-controllable constitutive expression of the transgene has been one of the urgent problems to be solved.