This paper discusses the measuring method and the measuring program of all of the dielectric, elastic and piezoelectric constants of ferroelectric single crystal (K0.20Na0.20Sr0.60Ba0.20)Nb2O6. This crystal was first grown by the authors. All 53 date of the dielectric, elastic and piezoelectric constants and some of the electromechanical coupling factors are published for the first time. Most of these date are measured in accordance with "IRE Standards on Piezoelectric Crystals" except that elastic coefficients S66 and S13 are measured by the thickness shear mode of the (zxl) 45° specimens and the length extensional mode of the (xzt) 45° bars respectively. The measuring accuracies are also discussed.