Praseodymium chloride (PrCl3) was encapsulated into channels of 1.4 nm diameter single-walled carbon nanotubes (SWCNTs) by a capillary filling method. The high-resolution transmission electron microscopy data demonstrated a high filling factor of the nanotubes and the formation of one-dimensional (1D) PrCl3 nanocrystals. The optical absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy data testified to the filling-induced lowering of the Fermi level of the nanotubes as a result of the electron transfer from the SWCNTs to the embedded PrCl3. The density functional theory modeling showed the absence of local chemical interactions between the nanotubes and the 1D crystals. It was found that the incorporated PrCl3 has stronger influence on the electronic properties of metallic nanotubes than semiconducting SWCNTs.