Abstract: The physical and mechanical properties of the wood of Yunnan pine (Pinus yunnanensis Franch) were influenced adversely by the occurance of cross grain as the present investigation indicated.The effect on the shrinkage in radial and tangential directions as well as in volume was not very obvious until the slope of the cross grain exceeding 20%,and became rather serious at the grain slope of 50%.Along the grain,the effect of cross grain on shrinkage was found much more noticeable.The grain slope beyond 20% increasing every 10% led the coefficient of shrinkage along the grain enlarging by 71%.Thus,the occurance of cross grain may be supposed tobe the main cause of developing bow or spring in the process of seasoningof a board. The cross grain in wood of Yunnan pine affected its mechanicalproperties to a great extent.The compressive strength parallel to the graindecreased by 14% when the grain slope beyond 20% increased every 10%,and decreased by 45% at the grain slope of 50%. The influence of cross grain on static bending strength of a beam was also not very obvious at the grain slope less than 10%.It decreased only 10% at the grain slope of 10%.Beyond the grain slope of 20%,the strength decreased by 56% with the increasing grain slope every 10% and decreased by 77% at the grain slope of 50%.As regards its modulus of elasticity,it decreased by 10% (average value for green and air-dried specimen) at the grain slope of 10%.It decreased by 54% as the grain slope beyond 20% increasing every 10% and decreased by 79% at the grain slope of 50%. Further,the impact toughness decreased by 10% (average value for green and air-dried specimen) and by 65% at the grain slope of 10% and 50% respectively.