To evaluate degree of reduction in shear moduli of sands with an increase in shear strain amplitude, dynamic soil tests were performed with use of hollow cylindrical samples applying torsional shearing forces. Two types of soil testing equipments, a resonant-column apparatus and a torsional shear apparatus, were employed. It is pointed out that shear moduli at shear strain amplitude of 10^-4 obtained from these two different equipments agree satisfactorily. Furthermore, extents of reduction in shear moduli with an increase in shear strain amplitude are shown for various sands. These data are compared with those presented by other investigators. On the basis of test results, a simplfied procedure for predicting reduction in shear modulus with an increase in shear strain amplitude is proposed.