We report here a novel multichannel closed-loop magnetically actuated microchip for high-throughput polymerase chain reaction (PCR). This is achieved by designing a series of concentric circular channels on one microchip and exploiting a magnetic force to drive DNA samples flowing continuously through the closed loops. The magnetic force arises from an external permanent magnet through ferrofluid plugs inside the microchannels. The magnet enables simultaneous actuation of DNA samples in all the channels. As the samples go around the loops, they pass through three preset temperature zones. Parameters of PCR, such as incubation time, temperatures, and number of cycles, can be fully controlled and adjusted. High reproducibility was achieved for different channels in the same run and for the same channels in consecutive runs. Genetically modified organisms (GMOs) were amplified simultaneously using the developed device. This simple, reliable, and high-throughput PCR microchip would find wide applications in forensic, clinical, and biological fields.