A purifier with molecular-rearranging device mainly includes a hollow tubular holder, a tubular molecular-rearranging device positioned in the tubular holder, a tubular isolating layer positioned in a bore of the tubular molecular-rearranging device, and two caps respectively having a through hole closed to two ends of the tubular holder. The purifier may be put around an exhaust pipe or a pipe for transferring liquid, so that a radiated magnetic field is produced by magnetic lines of the molecular-rearranging device and earth poles to magnetize and rearrange molecules of exhaust or liquid flown through the pipe, making the exhaust or liquid filtered and purified to reduce air and water pollution.