Studies of P in the soils of tropical humid regions have focused on evaluating the organic and available P forms in cultivated areas; however, little is known about the dynamics of the total and available P levels in areas of natural vegetation. In this study, we measured the total and available P content in native areas in the eastern Amazon and evaluated the relationship between these contents and soil attributes. The chemical and physical attributes and P content of the soils were analyzed. The total P was quantified by the EPA-3051 method, and the available P was extracted using ion exchange resin and Mehlich-1 (M1) and Mehlich-3 (M3) methods. The predominant soils were acidic, of low fertility, oxidic, and varying in texture from clay to sandy. The total P content was correlated in the following order, crystallized and amorphous oxide content > organic matter (OM) > silt > sand. The available P content was higher for M1, followed by M3, and resin for all soil classes. Mehlich was found to be an important extraction method, in addition to more consistent available contents, M3 can extract basic cations (K, Ca, Mg, and Na), there by optimizing laboratory analysis.