Abstract: The present invention relates to a process for producing a large architectural precast concrete panel for use in outside walls and applicable to the curtain wall technique of architecture, wherein a resinous substance and an inorganic material are placed in a mold, then a hydraulic cement composition is placed on the layer of above mixture. The polymerization of the resinous substance and the hydration of the cement composition are carried out in the mold simultaneously. A particularly preferred process employs the following critical conditions:1. The viscous methyl methacrylate syrup is one obtained by mixing about 100 parts by weight of viscous methyl methacrylate syrup with from about 0.5 to about 15 parts by weight of a radical polymerizable cross-linking monomer having .alpha., .beta.-unsaturated groups to obtain a resin solution;2. The particle size of the aggregates is between 0.6 and 15mm diameter;3.