Two types of hydraulic bilateral servomechanisms, symmetrical type and force-feedback type, are proposed and constructed. Characteristics of such bilateral servomechanisms are expressed by a square matrix with four elements which are functions of s. These four elements can be experimentally determined by two series of experiments: one with free slave-end and the other with fixed slave-end. For a symmetrical type the value of the determinant of the characteristic matrix is theoretically equal to the unity and independent of s.