Contamination of phosphorus (P) and arsenic (As) has drawn much attention in the past decades. Both P and As are predominantly present as inorganic oxyanions in both terrestrial and aquatic systems, i.e. as phosphate, arsenate and arsenite. The mobility and bioavailability of P and As are greatly influenced by the adsorption of their oxyanions to metal (hydr)oxides. Goethite is one of the most abundant iron (hydr)oxide minerals in natural environment. The adsorption of P and As by iron (hydr)oxides is strongly affected by pH. Apart from pH, natural organic matter (NOM), which frequently co-occurs together with oxyanions, plays an important role in influencing the adsorption of oxyanions. However, the composition and properties of NOM (e.g. particle size) often vary with the sources, which makes the understanding and prediction of oxyanion adsorption challenging. Because NOM contains large amounts of carboxylic and phenolic type of functional groups, which interact strongly with metal (hydr)oxides, we thus hypothesize that the site density of functional groups on NOM is the controlling factors influencing the adsorption of oxyanions at goethite-water interface. In this study, we investigated the adsorption of phosphate, arsenate and arsenite onto goethite in the absence and presence of NOM (four humic acids (HA), three fulvic acids (FA)) derived from different soils as a function of pH (pH 3-11), and surface loading of oxyanions or NOM. In combination with laboratory analysis, model calculation can reveal the whole fingerprint of surface speciation and can make predictions. Thus, the NOM-CD (CD: Charge Distribution) and LCD (Ligand and Charge Distribution) model were applied to describe these interactions and the performance of these two models were compared. Results show that the adsorption of oxyanions to goethite is decreased by the presence of NOM, especially for phosphate and arsenate at low pH. Effects of the three FA are similar, which are more effective than HA in reducing oxyanion adsorption at pH <6. Differences were observed between the four HA in their competition with oxyanions. The adsorption of phosphate, arsenate and arsenite in the presence of NOM are well described with both the NOM-CD and LCD model. The NOM-CD model is relatively simple to use, whereas the LCD model can better reveal different factors in the interaction, including the spatial distribution of adsorbed NOM on oxide surfaces. According to these two models: site density of carboxylic groups, protonation constant of carboxylic groups, and particle size of NOM are major properties of NOM determining its effect on oxyanion adsorption to oxides. At relatively low loadings, morphological change of adsorbed NOM takes place, and the degree of morphological change of adsorbed NOM depends on the particle size, site density of carboxylic groups and aromaticity of NOM. The influence of particle size on the interaction becomes more important at higher NOM loadings. The understanding obtained in this work can be used in the future to explain and predict the mobility of anionic pollutants such as P and As in soil and water, and to design pollution remediation measures in, e.g. groundwater, agricultural drainage, paddy field or waste water.