Silicon (Si), which mainly exists in soils as orthosilicic acid (H₄SiO₄), is beneficial for rice growth. In total, 17 Inceptisols soil profiles, 4 from uncultivated lands and 13 from paddy fields derived from felsic to ultramafic parent materials were collected for the extraction of available Si from horizon soil samples by using an acetate buffer solution. The aim of this work was to illustrate the relationship between extractable Si and general soil properties for predicting the availability of Si for rice growth. The means of available Si in the studied Inceptisols on the uncultivated lands and paddy fields were 244 mg kg⁻¹ and 114 mg kg⁻¹, respectively. The amount of available Si increased from the surface to subsurface soils in the soils on the uncultivated lands, whereas the available Si was irregular along with depth in the paddy soils. The amount of available Si was linearly and significantly (p < 0.001) correlated with clay and dithionite-citrate-bicarbonate extractable iron oxides (Fe_d) in all soils. The amount of available Si increased with an increase in pH in the soils from the uncultivated lands. However, a poor correlation was observed between pH and available Si in the paddy soils because labile Si was affected by human activities, such as liming and flooding, especially for surface soils. Nevertheless, the available Si was successfully estimated using crystalline iron oxides in the soils on the uncultivated lands; however, in the paddy soils, clay and organic carbon were used in the multi-regression model to estimate the amount of available Si.