For better understanding the mechanism regulating availability of phosphorus (P) in red earth, a study was carried out to investigate P fractions (Olsen-P; absorbed inorganic-P fractionated in Fe-P, Al-P, Ca-P, and O-P, and organic-P fractionated in labile, moderately labile, moderately stable and highly stable organic-P) in aggregates (>2 mm, 2～0.2 mm, 0.2～0.02 mm, 0.02～0.002 mm,＜0.002 mm) of upland and paddy red earths. Results indicate that in the upland soil about 72% of the aggregates were>0.2 mm, while in the paddy soil 67.5% were. In the two soils, inorganic P in aggregates>0.2 mm was dominated by Fe-P, but in aggregates<0.02 mm by O-P, while organic P in aggregates>0.2 mm and<0.002 mm in the paddy soil was much higher than that in the upland soil. In conclusion, the distribution of P in the soils of red earth was closely associated to particle size fractions of their aggregates, and the lower availability of P in the upland soil (P 3.9 mg g^-1, Olsen-P) as compared to the paddy soil (P 7.9 mg g^-1, Olsen-P) was presumably attributed to higher free-Fe and lower organic-P in its aggregates.