The effect of biosurfactantrhamnolipid alone and its combination with cation chemical surfactant cetyltrimethyl ammonium bromide (CTAB) on sludge dewaterability was investigated by determining the water content of dewatered cakes and capillary suction time (CST). When the rhamnolipid dose was 0.01 g·g-1 , the water content of sludge after centrifugation was lower by about 2.4% compared with raw sludge, while the water content of filtered sludge cake was lower by about 10.8%; but the value of CST increased from 27.3 s to 48.8 s. The results showed that the addition of the biosurfactantrhamnolipid could significantly promote the dewatering of sludge, but would slow down the dewatering rate of activated sludge. Compared with rhamnolipid or CTAB alone, the combination of rhamnolipid and CTAB (the combination proportion was 1∶1, 1∶2 or 1∶3) could not only decrease the water content of dewatered sludge cakes, but also improve the dewatering rate of activated sludge.