The method of an experimental determination of shear moduli of composites accepted as standards ASTM D5379/D5379M-12 and GOST R799-2015 has been considered. Its essential failings have been noted. It has been shown that a question of a correct selection of a method for an estimation of shear moduli of constructional materials, which can allow to determine their values reliably and with acceptable for practice accuracy is not solved until the present. Some other known methods of determination of shear modulus in the plain of the plate have been examined, in particular: a method of testing of tensile or compression of the three patterns carved from an orthotropic material in the directions to the main axis of its elastic symmetry and at an angle 45 to them; quadratic plates torsion test method carried out according to three-point loading scheme; and a method of testing of prismatic patterns on the four-point bending. The detailed analysis of borders of their acceptability and validity of values of determined characteristic has been realized using a wide range of constructional materials. Their worthiness and weaknesses have been indicated. It has been shown that during the usage of the first mentioned method, there can be a variant of determination of the shear modulus, which can be based on the values of and , which greatly simplifies the process of finding it. An easy device construction for the implementing the second the mentioned method has been offered; it helps make step loading and evaluation of deflections. Its usage allows obtain stable and reproduced characteristics without exploitation of any additional equipment. The modernization of the equipment used for fulfilling the third reviewed method has been made. It considerably simplified the precise setting of a pattern and gave an opportunity to realize an examination of a slim (1,5 mm and more) patterns without losing their stability in the transverse direction. The comparison of shear modulus determined by three different methods on the same constructive materials has been fulfilled. Their quite good coherence in all reviewed situations has been identified.