Abstract: Suspended particulate organic matter (SPOM) is one of the important components of organic matter in surface water, and plays an important role in the global carbon cycle and water eutrophication. Sequential extraction, carbon stable isotope (δ¹³C), three-dimensional excitation-emission matrix fluorescence spectra and parallel factor analysis methods were used to systematically study the content, components, fluorescence characteristics, sources and bioavailability of the SPOM in Lake Hulun in summer. The results indicated that the total amount of SPOM (measured by content of carbon) ranged from 14.4 to 31.5 g/kg, and extraction residue (HM) was the main component, accounting for 61.2% of the total SPOM. Three fluorescence components were found in water extracted organic matter (WEOM) in SPOM, including fulvic-like component C1, humic-like component C2 and tryptophan-like component C3. The contribution of humic component (C1+C2) and protein-like component C3 to the total fluorescence intensity was 70.4% and 29.6%, respectively. The values of C/N (ration of total organic carbon to nitrogen concentration) and δ¹³C in SPOM ranged from 7.53 to 15.2 and -27.2‰ to -26.1‰, respectively, indicating that the SPOM probably came from terrestrial sources. Based on the information of C/N and δ¹³C, similar results of the contributions of exogenous sources to SPOM (67.2% and 68.9%, respectively) were obtained. The HIX value of WEOM was between 4.09 and 7.40, with a strong degree of humification and poor bioavailability. However, the endogenous contribution to SPOM has gradually increased recently which may lead to enhanced bioavailability of SPOM and deserve more attention.