PURPOSE: To produce continuously a lightweight methacrylate polymer article having high fire resistance and a translucent beautiful appaerance, by extruding a mixture of a methacrylate-based polymerizable syrup and an inorganic filler.

CONSTITUTION: A mixture is formed from a methacrylate-based polymerizable syrup containing 10W40wt% methacrylate polymer (e.g., methyl methacrylate homopolymer or its copolymer with an α,β-ethylenically unsaturated compound), an inorganic filler (e.g., ettringite), a small amount of a thermosetting catalyst as a polymerization catalyst for the above syrup, and a photosensitizer. The titled article is obtained by extruding the mixture by an extruder, casting the surface of the extrudate by irradiation with light just after the extrusion and then curing the extrudate by polymerization. The obtained product is a polymer article comprising the methacrylate polymer, 20W80wt%, based on the total weight of the mixture, inorganic filler, the thermosetting catalyst, and the photosensitizer.