In this study, drying behaviour of medical plants such as fresh sweet basil, parsley and dill leaves in a vacuum heat pump dryer was investigated. Drying experiments were conducted at the vacuum pressure of 0.6 bar and the drying temperatures of 36 degrees C and 46 degrees C. Five thin layer drying models namely the Henderson and Pabis model, Logarithmic model, Two-term model, Modified page equation model and Lewis model to estimate moisture ratio of medical plants were used. Different mathematical drying models were compared according to their root mean square error, the coefficient of determination (R-2) and reduced chi-square Of (chi(2))For sweet basil, parsley and dill leaves, the logarithmic model, the Two-term model and the Henderson and Pabis model showed better fit to the experimental data compared to other models, respectively.