Abstract: Complexes in various size fractions from different fertility red soils obtained from Quaternaryred clay were separeted by ultrasonic dispersion in water. The various active organic phosphorus andphosphatase were analyzed in the paper. The results showed that the amount of organic phosphorus insoils and their complexes became larger with the increase of the fertility of red soils. The red soils andtheir complexes were dominantly involved in moderately active organic phosphorus (MAOP) and moder-ately stable organic phosphorus (MSOP), which were 80% of the total organic phosphorus. There was asignificantly positive relationship between soil phosphatase and soil complexes phosphorus.