Micromorphalogical characteristics of black soils,planosols and soda-solonchaks of various levels of fertility were investigated by means of structure analysis,optical microscopy and scanning electron microscopy.The results are summarized as fallows:1.With large amount of humic substances,black soils are well aggregated and highly stable in structure.The content of microaggregates(>0.05 mm) in black soils is about 30-70%,that in planosols is less than 30%,that in unimproved soda-solonchak is 20%,and that in ameliorated soda-solonchak is 46%.The water-stable aggregates (>0.25 mm) are distributed with the same tendency of the microaggregates(>0.05 mm) in the soils.2.Under microscope,the degree of aggregation and the size of soil microaggregates,as well as soil porosity can be observed precisely.Black soils have a spongy fabric.Soil particles are cemented by gel-like substances to form porous soil structure.Planosols show a loose bound agglomeratic fabric with lower porosity.Unimproved sodasolonchaks belong to a porphyropeptic fabric in which almost no aggregates can be found.The ameliorated soda-solonchaks have a pluctoamictic fabric in which microaggregates are formed by the gel-like subatances and mineral grains.3.The variation of the organo-anineral complexes in soils is also observed by scanning electron microscope.In fertile black soils the organo-mineral complexes are agglutinated by the gel-like substances to fbrm a loose and soft soil structure.In unimproved soda-solonchaks and planosols the particles are merely accumulated together without any evidence of eementation.While in ameliorated soda-solonchaks some gel-like substances appear on the particle surface,which means organo-mineral complexes are formed.