Diffraction tomography provides a good method for reconstructing cross-section images of weakly scattering dielectric objects. The Born and Rytov approximations are well-known approximations for the first-order diffraction tomography method. In this paper, the restrictions of the Born and Rytov approximations are experimentally investigated when the object is immersed in a medium. Microwave tomography images of several kinds of dielectrics of different shapes and dielectric constants are imaged both in the air and in the sand. It is shown experimentally from the resultant images that the Born approximation produces a better estimation for objects small in size and even for objects of large deviations in relative refractive index; on the other hand, Rytov approximation gives a more accurate estimation mainly for objects with small deviations in relative refractive index. The Rytov approximation is also valid for large-sized objects if the first condition is satisfied. The results also show that it is possible to image objects located in medium by the diffraction tomography method and that the method can be applied in biomedical and NDT applications.