To provide a method for manufacturing fine copolymer particles that show little precipitation in a dispersion and are easy to manufacture and to handle, and to provide a sheet material that shows no adhesion when piled under a highly humidity, and has a hydrophilic binder layer comprising fine copolymer particles that do not come off both in dry and wet handling.

A mixture of 0.5-4 mass% of an ethylenically unsasturated monomer having a carboxylic acid group, 0-20 mass% of an ethylenically unsaturated monomer having a nonionic, hydrophilic group and 76-98.5 mass% of a hydrophobic, ethylenically unsaturated monomer, is subjected to suspension polymerization in an aqueous medium in the presence of a water-soluble cellulose. The fine copolymer particles are formed by adding a water-soluble polymerization initiator to the aqueous medium after the polymerization.