The ethylene glycol monoethyl ether method was used for determining the surface area of 43 soil samples in the following conditions: original soil, soil deprived of the organic matter and soil from which the organic matter and free iron oxides were removed. The effects of various exchangeable cations, organic matter and free iron oxides upon surface area of soils were studied. It was possible to estimate the apparent surface area of the organic matter on about 827m2/g. The calculated surface area of iron oxides varied between 77 and 235 m²/g, with an average value of 159 m²/g.