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To explore a possible phosphorus limitation of soil microbial processes, we fractionated phosphorus in Japanese forest soils (10 Inceptisols, three allophanic Andisols, seven nonallophanic Andisols, and one Spodosol) by sequential extraction into inorganic P (Pi) and organic P (Po) in H 2 O, 0.5 M NaHCO 3 , 0.1 M NaOH, 1 M HCl and conc. HCl fractions, and total P in residual fractions. NaOH-Pi and NaOH-Po fractions were the largest P components in all soil types. Apart from H 2 O-Pi, NaOH-Pi, and NaOH-Po, P concentration in each fraction did not differ significantly among soil types. Concentrations of P in fractions H 2 O-Pi, H 2 O-Po, 0.1 M NaOH-Pi, 0.1 M NaOH-Po, and residual P were correlated with active Al, but not with active Fe, indicating a more significant contribution of Al in controlling P forms in the soils. The proportion of available P (H 2 O + NaHCO 3 j P) to total P was negatively affected by active Al and Fe contents and by pH in the soils. High phosphomonoesterase and phosphodiesterase are known to be indicators of low soil P availability, and both activities were higher in soils with low available P in this study, suggesting that microorganisms of these forest soils may be P limited.