A TGA assisted hydrothermal process was employed to prepare chalcogenide nanorods. The different morphology of CdS nanomaterials prepared with and without the TGA assisted hydrothermal process indicates that TGA plays a critical role in controlling the nucleation and growth of CdS nanomaterials. The paper makes a preliminary presentation of the mechanisms of preparation of chalcogenide nanostructures with and without the use of the TGA assisted hydrothermal synthesis. FeS nanorods and nanoparticles have been prepared by the TGA assisted and without the TGA assisted hydrothermal process, respectively, which confirmed the proposed mechanism. X-ray diffraction (XRD) shows that the nanorods are of orthorhombic structure, and selected area electron diffraction (SAED) pattern showed that the FeS nanorods were single crystalse. Further investigation for the synthesis of other chalcogenides will be undertaken in order to confirm the proposed mechanism.