The authors chose magnetotactic bacteria of the loess-paleosol sequences of China as a target and made successive studies on magnetotactic bacteria in layers of Duanjiapo section, layers of Xifeng section as well as S5-1 layer in Luochuan section by such means as TEM, SEM, biochemical experiments, and organic geochemistry.The results show that they consist of membrane and cytoplasm as well as magnetosomes and gas balls arranged along long axes. Under the suitable conditions, a lot of magnetosomes grow in the magnetotactic bacteria. Magne- tosomes consist of Fe2O3·H2O, and can be discharged from the bacterial bodies to surrounding environment. This can change Fe2+to Fe3+and increase magnetic susceptibility in the layers, especially in the paleosol layers. The product of magnetotactic bacteria in the loess section of China is a function of temperature, humidity, pH value and content of iron at the surface. They are obviously different from magnetotactic bacteria in the lake and swamp in shape, quantity and arrangement of magnetosomes, and hence the magnetotactic bacteria in loessial re- gion of Northwest China constitute a typical ecological species.