One-dimensional (1D) hierarchical nanostructures of ultralong layered KxMnO2 (x < 0.3) bundles with diameters 50-100 nm and lengths up to 50-100 Am have been successfully prepared by a PEG-assisted hydrothermal method based on the reaction of KMnO4 with 2-ethylhexanol. The obtained samples ascribe to the monoclinic phase and exhibit ferromagnetic behaviors below 32 K and paramagnetic behaviors above 32 K, which may make this system a promising base material for magnetic devices. A series of contrastive experiments have illustrated that 2-ethylhexanol, PEG 400, KOH, and reaction time play an important role in the synthesis of the nanobundles. A possible growth mechanism has been proposed.