Abstract: The biodegradation efficiency of two petroleum-degrading strains SY1 and SY2 was investigated with synthetic seawater. Experimental results indicated that their biodegradation rates were 41.3% and 42.6% respectively without addition of minor nutrients. Both the strains can adapt to typical ocean conditions including temperature, pH and dissolved oxygen, and also degrade a broad spectrum of hydrocarbon substrates. The kinetic model of biodegradation of crude oil by these two strains were also established, which abides by Michealis-Menten equation.