Abstract: A board composed of a lignocellulosic material and the modification thereof as the substantial components and having good mechanical strength, even when the board does not contain any components derived from an additive, by utilizing the autoadhesion of a specified lignocellulosic substance. This board is produced by molding under heat and pressure a lignocellulosic substance containing at least 30 weight % of a malvaceae bast plant, being substantially free from any component derived from an adhesive, and has a strength value of more than 100 as defined by the following formula (I): 0.48.times.Y/X.sup.2, wherein Y is a bending strength (kgf/cm.sup.2) and X is a density (g/cm.sup.3). A particulaly preferable example of the plant is the kenaf.