The basic property "shear modulus" (G) of 84 old timber beams is investigated. G is important for short timber members or for parts subjected to torsional action. The calculation of the G and Modulus of Elasticity (MOE)/G ratio is based on transverse vibration technique, easy to be applied. Results: the average value of MOE/G is 21; the relationship with knots is weak; the time seems to have no effect on G, as on wood, in absence of decay and damages.