Phosphorus (P) is usually enriched in urban soils but the environmental consequences of this P enrichment are not well understood. The objective of this study was to investigate P sorption characteristics as a measure of potential P loss from urban soils due to P enrichment via runoff and leaching. We collected soil samples at 0–5 and 5–15 cm soil depths from urban park areas in Nanchang, China, a rapidly expanding city with low P contents in its natural soils. Soil P sorption indices were characterized by a multiple-point isotherm batch experiment. The 0–5 cm layer had lower Langmuir P sorption maximum (Smax) than the 5–15 cm layer, probably because of its lower amorphous Al oxide (Alox) content and higher soil organic carbon (SOC) content. Stepwise multiple regression showed that the combination of Alox and SOC were the two most important soil properties related to Smax of the studied soils. A two-piece segmented linear regression was fitted to the relationships between labile P fractions (i.e., water extractable-P and anion exchange resin-extractable P) and binding energies (k) and the change point values were identified for k below which labile P decreased linearly. Soils below the change point had greater contents of SOC and exchangeable Ca and Mg and higher pH than those above the change point. These results suggest that parent materials played a major role in regulating P sorption capacities of the urban soils, particularly for the soils in urban green spaces. However, the enrichment of Ca and Mg derived from dissolution of calcareous materials in urban areas could significantly influence P bonding strength and saturation ratio of urban soils.