In this paper, the effects of knots on physical and mechanical properties of wood systematically were summarized. In general, effects of knots on physical and mechanical properties of wood depend on three factors; deviation of wood fibers surrounding the knots from longitudinal axis, fibers of knots which are perpendicular or a definite angle to wood fıbers and erneking due to cxtrcme shrinkage of the knot woods during drying. Results of studies expressed that density, shear strength and hardness of wood specimens increased as knot area in the cross sections inereased. But, sorption (shrinkage and swelling), modulus of elasticity in bending, bending strength, comppression strength and impact bending decreased.