This invention relates to a process for making dimensionally stable reconstituted composite products from lignocellulosic material. By treating lignocellulose with high pressure steam to decompose and hydrolyze the hemicellulose, cellulose and lignin fractions of the lignocellulose and using those decomposition products as both a bonding and bulking agent, it converts, under heat and pressure in a molding operation, the treated lignocellulose into molded composite products such as panel boards and molded articles. The composite products thus produced possess good physical and mechanical properties. Specifically, the dimensional stability in terms of the thickness swelling and linear expansion of panel boards such as fiberboards and particleboard, can be minimized to very low levels when the panel boards are made in high density. The adhesive bond developed from thermosetting of the decomposition products of hemicellulose, cellulose and lignin is strong and stable, and resistant to boiling water and acid hydrolysis, and is free of formaldehyde emissions. Thus, the reconstituted panel boards and molded products are suitable for exterior and particularly for indoor applications. The absence of free formaldehyde emissions makes the product very suitable for interior applications. The manufacturing cost for the reconstituted products is significantly lower in comparison to the conventional process because expensive synthetic resin is not used.