To provide a dewatering aide which allows biological decomposition utilizable as raw material of compost and a dewatering method using the same.

This dewatering aide comprises natural fiber 100 pts.wt. having a thickness of several μm to 1 mm and a length of 1 mm to several cm and water soluble natural polymer chemical 2-10 pts.wt. Further, in this dewatering method of liquid waste, the natural fiber is the remains of plant, the water soluble polymer chemical is biodegradable one such as carboxymethylcellulose salt, alginic acid salt and polyvinyl alcohol and, further, the dewatering assitant is added to liquid waste and is mixed and, thereafter, dewatering treatment is performed.