An acrylic SMC or BMC, in which when a polymer powder (C) having a bulk density in the range from 0.1 to 0.7 g/ml, an oil absorption of lin-seed oil in the range from 60 to 200 mi/100 g, a degree of swelling by methyl methacrylate is 16-fold or more and a specific surface area in the range from 1 to 100 m2/g is added as a thickening agent, hot water resistance is improved by using a polymer powder (C1) containing no surfactant, a polymer powder (C2) containing as a constituent component a reactive surfactant, or thickening speed is controlled by using a non-cross linked polymer powder (C3) having a Mw from 100,000 to 2,500,000, a non-crosslinked polymer powder (C4) having a Ma from 2,500,000 to 5,000,000, a crosslinked polymer powder (C5) and a polymer powder (D) having a specific surface area from 0.01 m2/g to 1 m2/g; a production method thereof; a method for producing acrylic artificial marble in which components are extruded by a kneading extruder (9) into given shape; and a thickening agent.