γ-Fe2O3 nanoparticles were successfully synthesized by a chemically induced transformation of α-FeOOH.In this method,the precursor(α-FeOOH)was prepared by chemical precipitation,and then treated with a mixed FeCl2/NaOH solution to produce the nanoparticles.X-ray diffraction indicated that when the precursor was treated with FeCl2(0.22 mol/L)and NaOH(0.19 mol/L),pure γ-Fe2O3 nanoparticles were obtained.However,when the concentration of FeCl2 was<0.22 mol/L or the concentration of NaOH was<0.19 mol/L,α-FeOOH and γ-Fe2O3 phases co-existed in the nanoparticles.Transmission electron microscopy observations showed that in the samples with co-existing phases,the nanoparticles did not have identical morphologies.The pure γ-Fe2O3 nanoparticles were polygonal rather than spherical.The volume ratio of α-FeOOH and γ-Fe2O3 was estimated for the two-phase samples from magnetization data obtained from a vibrating sample magnetometer.This chemically induced transformation is novel,and could provide an effective route for the synthesis of other metal oxide nanocrystallites. γ-Fe2O3 nanoparticles were successfully synthesized by a chemically induced transformation of α-FeOOH.In this method, the precursor (α-FeOOH) was prepared by chemical precipitation, and then treated with a mixed FeCl2 / NaOH solution to produce the nanoparticles. X -ray diffraction indicated that when the precursor was treated with FeCl2 (0.22 mol / L) and NaOH (0.19 mol / L), pure γ-Fe2O3 nanoparticles were obtained. concentration of NaOH was <0.19 mol / L, α-FeOOH and γ-Fe2O3 phases co-existed in the nanoparticles. Transmission electron microscopy showed showed in the samples with co-existing phases, the nanoparticles did not have identical morphologies.The pure γ-Fe2O3 nanoparticles were polygonal rather than spherical. The volume ratio of α-FeOOH and γ-Fe2O3 was estimated for the two-phase samples from magnetization data obtained from a vibrating sample magnetometer. This chemically induced transformation is novel, and could p rovide an effective route for the synthesis of other metal oxide nanocrystallites.