Paddy field converted into forest land is very common in southern China in recent years. In order to understand the effects of this change on soil minerals (soil clay minerals and iron oxides), A series of paddy and forest soils in Zhejiang Province were selected, and the evolution of the morphology and quantity of iron oxides were studied by using a combination of field investigation and laboratory analysis. The results showed that the morphology and spatial distribution of soil iron oxides changed significantly after land-use change. The content of total iron did not change significantly; free iron in the surface and subsurface soils increased slightly, other layers changed insignificantly; after planting trees for 15 - 20 a, amorphous iron in 4 soil series fell down between 18.0% - 38.4% and 24.7% - 48.9%; the ratio of crystal to colloid of iron oxides in surface soil increased by 0.73 to 1.62 times; soil ferrous iron decreased significantly, which was up to 95.8% at most; complex iron fell down between 21.3% and 36.2%, and significantly correlated with organic matter (P<0.01). The relative content of chlorite and the ratio of chlorite to kaolinite in subsurface soil decreased, while the changes of other clay minerals were unobvious. Soil organic matter decreased significantly, soil was acidified obviously after the conversion, the morphology of soil iron oxides changed obviously. The change of the morphology and quantity of soil iron oxides had important effects on soil structure, the migration and transformation of soil heavy metals.