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As an important geomorphologic element of the coastal areas, lagoons receive relatively less attention than estuaries and deltas in the NW Pacific marginal sea. In this study, based on proxies of delta C-13, pollen and diatoms from a sediment core, we attempt to understand the Holocene sedimentary environment of the Songji lagoon, South Korea, and the possible mechanism for its response to global or regional sea level and climate changes. The sedimentary environment was phased in different periods: an estuary, an estuarine lagoon, an intermediate environment, and an intermediate to brackish lagoon in early Holocene to 6.7 cal kyr BP, 6.7-6.3 cal kyr BP, 6.3-4.5 cal kyr BP and 4.5-1.3 cal kyr BP, respectively. Afterward, abundant freshwater entered the lagoon from the stream. The environmental evolutions were triggered by sea level and climate changes. The fluctuation of the sedimentary environment implies that the sea level rose from 4.5 to 2.2 cal kyr BP, and declined from 2.2 to 0.8 cal kyr BP. The sedimentary environmental change is also probably connected with El Nino activity, especially in the periods 6.7-6.3 cal kyr BP, 4.5-3.6 cal kyr BP and 3.0-2.0 cal kyr BP.