In this paper, we evaluated the seasonal variations of particulate and dissolved organic carbon and explored their sources in Lake Bosten. Water samples were collected at 13 sampling sites during May, August and October in 2012. Particulate organic carbon(POC), dissolved organic carbon(DOC), particulate organic nitrogen(PON) and chlorophyll-a concentrations were analyzed. On average, the POC concentration in the autumn(1.58 mg/L) was 2.2 times and 2.5 times of that in the summer(0.71 mg/L) and spring(0.64 mg/L), respectively. Larger seasonal variation of POC was found in the northwest and central areas whereas eastern lake revealed relatively small seasonal variation of POC. External sources were responsible for the variability of POC in the spring and autumn, but plankton made a considerable contribution to POC in the summer. Overall, the concentration of DOC was lower in the summer than that in the spring and autumn. The average DOC concentration for the whole lake was about 10.3 mg/L in the spring and autumn and 9.3 mg/L in the summer. Unlike POC, DOC showed the largest seasonal change in the river mouth and the smallest change in the central area of the lake. The contribution of allochthonous organic carbon to DOC was probably much bigger than that of autochthonous organic carbon in Lake Bosten.