Technical Abstract: Information on the chemical composition of sediment phosphorus (P) is fundamental to understanding P dynamics and eutrophication in lake ecosystems. In this study, P compounds were investigated in the sediments of seven lakes representing two contrasting ecological areas in China: the middle and lower reaches of Yangtze River region and Southwestern China Plateau each with serious eutrophication conditions. Sediments were extracted by NaOH–EDTA, and extracts were analyzed by 31P NMR spectroscopy. Results show that the extracts were dominated by inorganic orthophosphate (76.7–97.4% of the extracted P) and orthophosphate monoesters (1.8–14.3%), with smaller amounts of orthophosphate diesters (0.4–8.9%), pyrophosphate (0.1–0.7%) and phosphonates (0.1–0.2%). DNA-P was the major constituent of diesters, with its presence associated with sediment bacteria. There existed significant differences in the occurrence of orthophosphate and monoesters in different lakes. The relative distribution of orthophosphate for hypertrophic or shallow lake sediments was higher than that for eutrophic and mesotrophic or deep lake sediments, while the relative distribution of monoester P was the opposite. This research improves our understanding of the P cycle in lake ecosystems.