Maghemite, γ-Fe 2 O 3 , has regained importance as a magnetic tape storage material for the big data era due to its low cost and long-term durability. However, the conventional synthesis of γ-Fe 2 O 3 , which involves dehydration, reduction, and oxidation processes, is complicated and requires improvement. We synthesized γ-Fe 2 O 3 directly via dehydration from the high-pressure phase of iron hydroxide, ϵ-FeOOH, using a low-temperature solution method. Bulk ϵ-FeOOH prepared from α-FeOOH at 8.2 GPa and 773 K transformed into γ-Fe 2 O 3 in a 2-phenoxyethanol and LiOH•H 2 O mixture at 498 K, which is the lowest temperature among similar dehydration reactions. 57 Fe Mossbauer, Raman, and Fourier transform infrared spectroscopy analyses revealed that the obtained γ-Fe 2 O 3 particles were covered with amorphous lithium phases, which stabilized their ferrimagnetism with a magnetization of 61.9 emu g −1 up to 1273 K, by converting to ferrimagnetic Li 0.5 Fe 2.5 O 4 . Furthermore, we reduced the size of γ-Fe 2 O 3 to an average of 0.5 μm and a minimum of approximately 100 nm by applying ϵ-FeOOH nanoparticles as a precursor, which were prepared under higher-pressure (10 GPa) and lower-temperature (673 K) conditions. Although synchrotron X-ray diffraction measurements found that the γ-Fe 2 O 3 nanoparticles were contaminated with ion-exchanged α-LiFeO 2 at 80 wt %, a facile and low-temperature method to synthesize γ-Fe 2 O 3 was established.