The loading of single-walled carbon nanotubes (SWCNTs) is very important for applications. Loading methods include loading from the gas phase, as well as the liquid phase— melted compounds and solutions. It was demonstrated that the incorporated substances form new, interesting properties and phases inside SWCNTs. Spectroscopic techniques, such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), optical absorption spectroscopy (OAS), and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), were utilized. It was shown that the incorporated substances may cause the p- and n-doping of the SWCNTs. I have encapsulated new compounds, such as iron chloride (FeCl₂), cobalt chloride (CoCl₂), and bismuth telluride (Bi₂Te₃), inside SWCNTs. The loading was investigated by high-resolution transmission electron microscopy (HRTEM), and it was proven that the interior space within the SWCNT walls was loaded. The incorporated substances formed crystalline phases inside the SWCNTs. The spectroscopic investigations showed that iron chloride and cobalt chloride led to p-doping of the SWCNTs. This was observed as the changes in the shapes of the Raman modes, shifts in the C 1s XPS on the lower-binding-energy side, the appearance of additional peaks in the C 1s NEXAFS, and the disappearance of peaks in the OAS spectra.