To obtain a sheet-forming composition that can provide formed sheets that can utilize crushed products as waste rubber or the like and can form sheets having practical strength and durability by mixing crushed products as waste rubber with rubber latex and the like.

The sheet-forming composition is produced by mixing (A) a crushed rubber waste and/or crushed plastic waste, preferably they are foamed, with (B) a rubber latex and/or a resin emulsion, preferably at a weight ratio A/B of 5-20. In a preferred embodiment, the rubber latex of the component B is a chloroprene rubber latex having the value of G=0 in the formula G (in %) = (W0/Wi)×100 [G is the fraction insoluble in chloroform in %; Wi is the weight (in g) of the film formed by casting a chloroprene rubber latex; W0, is the dry weight (in g) of the insoluble part that remains on the wire screen of 200 meshes after dissolving the film in 5% concentration of chloroform].