PURPOSE: To prepare a decorative board closely resembled to a natural wood without requiring conventional complicated works by a method wherein a special printing ink containing a foaming agent and a coloring pigment or the like is printed on a surface corresponding to a spring wood grain and an autumn wood grain of a base board subjected to undercoating treatment and, thereafter, passed through a foaming and a drying procedure.

CONSTITUTION: A printing ink containing a foaming agent such as an azo type compound with a foaming ratio 2W5 times and a coloring agent mixed in a known vehicle with low oil absorption is printed on a part 3a corresponding to an autumn wood grain of a surface of the base board 1 applied with an undercoating treatment layer 3 of a known natural resin or the like according to necessity and a printing ink containing a coloring pigment and/or a body pigment with a large particle size as well as having a high oil absorbing property is printed on a part 3b corresponding to a spring wood grain thereof and, subsequently, a transparent or a semitransparent top coating resin 4 with high permeability and a low viscosity is painted and the foaming of the resin and the drying of the paint are carried out by a hot air furnace or the like. Thereby, the decorative board 5 having the decorative layer 3 closely resembled to a natural wood is prepared.