PURPOSE: To obtain a medium comprising an interlaced material of a biodegradable synthetic polymer fiber, capable of being readily supplied in a short time, having no anxiety of incineration and abandonment, excellent in environmental protection, saving of labor and execution, useful for culturing natural lawn grass, etc.

CONSTITUTION: This medium comprises an interlaced material comprising one biodegradable synthetic polymer fiber selected from -caprolactone/-caprolactam copolymer, a polycaprolactone, an aliphatic polyester and a composite material of these polymers and cellulose, having 1-30 denier of single fiber fineness and 0.01-0.2g/cm3 fiber density. A pile for artificial lawn grass preferably comprises a filament or a film composed of the biodegradable synthetic polymer fiber and an artificial lawn grass structure is produced by using the pile.