The mathematical model describing the course of drying curve of single parsley root particles under conditions of natural convection was formulated on the basis of the general theory of heat and mass transfer laws. The course of the drying curve was described in two ways: using the linear model of the first drying period (without shrinkage) and then using the models of second drying period and the models of first drying period taking into account shrinkage and finally the models of second drying period. The second drying period was described in both cases by the same models which approximated the shape of dried particles as follows: infinite plane (slices cut crosswise and along the root, axial cylinder slices), finite cylinder (slices cut crosswise the root, axial cylinder slices), finite in two dimensions plane (bark rings), infinite cylinder (bark rings). The verification confirmed that the following mathematical models describe the course of drying curve with satisfactory accuracy: for crosswise and lengthwise slices and axial cylinder slices-the linear model or models with shrinkage in the first drying period and the model of infinite plane in the second drying period, for bark rings-the linear model or models with shrinkage in the first drying period and the model of finite plane in the second drying period. The models with shrinkage in the first drying period and the model of finite plane in the second drying period. The values of relative error were not higher than: 1% for linear model, 4% for models with shrinkage, 29% for models of the infinite and finite plane drying. The results of modelling pointed out the need of the model formulation of moisture content changes in parsley root particles dried in transition period. Obtained results allowed of the statement that parsley root can be regarded as an anisotropic and heterogeneous body.