To provide a biodegradable water-absorbing material which is excellent in biodegradability, inexpensive, good in water absorption and also has a high heat-resistance at a swollen state and water retainability at a high temperature and can be used as a suitable composting aid.

The biodegradable water-absorbing material is characterized in that the material is prepared by introducing hydrophilic groups to starch lees containing 26-90 mass% starch in terms of dry mass and subjecting the resultant material to crosslinking. Starch lees being low in utility value can be used effectively.