Molecular diagnosis is the most powerful method to analyze genetic diseases, cancer and viral infectious disease. The most representative method of molecular diagnosis is polymerase chain reaction (PCR). The PCR process repeats cycle of temperature change of denaturation(95℃) annealing(55℃) and extension(72℃). Conventional PCR machines require a long experiment time because they change the temperature of heating block with large heat capacity. In this study, we developed ultrafast microfluidic chip based closed-loop circulation system for PCR. We developed a closed loop circulation system using an internal micro pump. The internal micro pump consists of a pumping chamber, an oscillating magnetic bar and an external motor with magnets. We obtained a result of 4 seconds for one cycle time with 15μl of reagent, and successfully amplified the DNA in the microfluidic PCR devices using closed-loop circulation system in 20min.