Knots are one of the main natural defects that affect wood utilization.The authors sought to have a better understanding how knots affected glue laminated board performance by testing and analyzing the shear modulus of 100 mm×88 mm×48 mm Pinus sylvestris samples with different knot types and size.The results showed that knots present in the gluing surface influenced the bonding.Generally,knot size had more effect than the knot type on shear strength.The conclusion is that knots with diameter more than 25 mm significantly reduced the shear strength and should be removed.