【Objective】Selenium (Se) is an essential micronutrient for human and animals. Ingestion of either an inadequate or excessive amount of Se tends to lead to health problems. Bioavailability of Se in soils depends on its forms. Iron oxides and humic acid are important components of soils and may interact with Se through desorption/adsorption. Iron oxides and humic acid in soils are often cemented together forming aggregates, thus significantly affecting translsocation and transformation of nutrient elements and contaminants in the soils. However, in-depth knowledge about the effects of iron oxides-humic acid complex on speciation and bioavailability of Se in soils is still rarely available. 【Method】In this study, goethite-humic acid complex was prepared through a modified co-precipitation procedure for analysis of selenite (Se(IV) adsorption characteristics in aqueous solutions through a series of tests, like pH, Zeta potential and X-ray photoelectron spectrum(XPS) and isothermal adsorption. 【Result】 At the initial pH=4, the adsorption capacity (Q_m), as fitted with the Langmuir model, was 0.202 mmol g^-1 and 0.159 mmol g^-1 for goethite and the complex, respectively. The Langmuir model was suitable for use to describe isotherm adsorption of Se(Ⅳ) for goethite (R²=0.970), while the Freundlich model was for the complex (R²=0.980). As for goethite and the complex, the isoelectric point (IEP) was about 7.0 and less 3.0, and zeta potential at pH=4.0 was 46.6 mV and -40.5 mV, respectively. X-ray photoelectron spectrum (XPS) showed that the electronic binding energy (B.E.) of the Fe2p_3/2 on the surface of goethite and the complex was 711.4 eV and 711.5 eV respectively, and the B.E. of the C1s on the complex surface was 284.8 eV. With the initial pH being 4.0, changes in interactions between the samples and Se(Ⅳ) were embodied mainly in the following aspects: (1) pH rose up to 4.4 and 4.2, respectively in the suspensions of goethite and the complex, while surface potential decreased by 39.08 mV in goethite, but increased by 1.8 mV the complex; (2) B.E. of Fe(Ⅲ) dropped by 0.4 eV on the surface of goethite, but remained almost unchanged in adsorbed Se(Ⅳ); (3) B.E. of Fe(Ⅲ) decreased by 0.3 eV on the surface of the complex , but increased by 0.6 eV on adsorbed Se(Ⅳ), and the B.E. of C in C-O bonds rised to 286.5 eV. 【Conclusion】The complex is lower than goethite in Q_m of Se(Ⅳ) and affinity for absorbed Se(Ⅳ). But their adsorptions of Se(Ⅳ) occur mainly through the following mechanisms, i.e. surface coordination reaction and hydrogen bonding. The electrostatic attraction would contribute to improve the Q_m of Se(Ⅳ) on goethite, while the electrostatic repulsion was the reason that decreased the Q_m of Se(Ⅳ) on complex. Moreover, for surface coordination in the complex, bidentate coordination existed between iron hydroxyl groups (≡FeOH) on the surface of the complex and HSeO₃^-. In addition, the adsorbed Se(Ⅳ) on the surface of the complex interacted with both goethite and humic acid, forming a goethite-Se(Ⅳ)-humic acid ternary system.