PURPOSE: To prepare a novel thermosetting slurry composition giving a flexible coating film having excellent appearance such as smoothness, gloss, etc., and applicable without necessitating waste water treatment, by dispersing a powder coating based on a thermosetting resin in a plasticizer.

CONSTITUTION: To a base resin such as an acrylic copolymer having glycidyl group is added a crosslinking agent such as polybasic carboxylic acid compound, amine compound, etc., pigment, and a leveling agent, and if necessary, a crosslinking reaction catalyst, etc., and the components are mixed in dry state. The mixture is molten and kneaded with an extruder, cooled, and pulverized to an average particle size of preferably 5W20μ to obtain a powder coating. The coating material is mixed with a plasticizer such as phthalic acid esters, phosphoric acid esters, etc. at a weight ratio of preferably 30:70W70:30 to obtain the objective slurry composition.