The charge characteristics of the clay fraction of red soils under present investigation are summarized as follows:(1) The clay fraction of red soils carries a smaller amount of negative charge, but a greater amount of positive charge than that of neutral soils of temperate regions. The humus of the clay fraction of red soils has smaller calculated "apparent negative charge" than that of neutral soils, but it gives a relatively large quantity of negative charge to the entire clay. These characteristics are more significant for certain laterites.(2) The electric charge carried by the clay fraction of red soils varies distinctly at different pH and in different soil types. For a red soil derived from Quarternary red clay in central China, a variable negative charge appears at soil acidity strenger than pH 5, and a negative adsorption of chloride takes place at pH above 6. The laterite carries net negative charge at higher pH and net positive charge at lower pH with an isoelectric point of about pH 4. In the laterite isoelectric point increases after the removal of humus but decreases after the removal of humus and tree iron oxides.The vanability of electric charge of the red soils derived from granite in southern China lies in between that of the above-mentioned soils.