Flow-through polymerase chain reaction (PCR) microfluidic systems for fast, small-volume DNA amplification on a single chip are significantly impacting medical and bioanalytical research. We have fabricated an improved, practical flow-through PCR chip by weighting a pressure-sensitive polyolefin (PSP) film onto a cyclo-olefin polymer (COP) substrate. The substrate was cut so as to produce microchannels, and was used to amplify DNA using a small moving liquid plug, in contrast to conventional continuous-flow-through PCR. Infrared (IR) imaging-based thermal analysis of the PSP film enabled the gradient and uniformity of the rapidly flowing microfluid to be accurately visualized, because the PSP film is thin, transparent and heat resistant. The liquid plug flow-through PCR, operating at 150 µl min(-1), showed approximately 55% amplification compared to a commercial PCR instrument, and required only 250 s for 40 cycles. To our knowledge, this is the fastest cycling time reported to date. In a real test sample, the liquid plug flow-through PCR could detect the presence or absence of anthrax in a sample solution in approximately 250 s. Thus, this liquid plug flow-through PCR system, based on our novel PCR chip, excelled in a practical applications compared to other devices.