The study relates to questions of rheological formulation in phenomenological aspect. The authors present a summary of the theory of mechanical models of linear viscoelastic centres and the method of the experimental rheology, and also the results of own investigations on the rheological propriety of various high-hydrated plant materials (apples, roots: vegetables and beetroots, tubers of potatoes). The investigations were realised on a test stand designed specifically for this purpose. The strength tests were conducted by subjecting samples of the material to loading between two parallel plates, maintaining constant stress (the creep test), recording their deformation until the achievement of constant speed of the creep (so-called steady creep); then the load was removed and the return of the deformation was observed, until the moment of its stabilisation at a constant level. The Burger's model was assigned to studied objects, and the parameters of estimation the of rheological properties  were the modulus of elasticity E, the coefficient of internal friction K and the ratio of the return deformation to the creep deformation. It was found that the adopted level of loads for the various groups of objects (apples, roots of vegetables, roots of red beet, tubers of potatoes) was correct from the viewpoint of comparative analysis, because the ratio of return deformation to creep deformation was in all cases within a similar and significant range of about 50-70%, and the K parameter for the particular groups of studied objects fell within the following ranges: for apples 219-345 MPa·s, for vegetables 680-1199 MPa s, beetroots 1700-1375 MPa s, tubers of potatoes of Salto variety 654-855 MPa s. The roots of carrot and red beet were characterised by the highest modulus of elasticity E.