The effect of carbon precursors on the formation of 0.4 nm single-walled carbon nanotubes (SWNTs) in one-dimensional channels of AlPO-5 single crystals was studied by means of Raman spectroscopy. Among more than ten carbon precursors which can be used in the fabrication of 0.4 nm SWNTs in the channels, the precursor of tetrapropylammonium-hydroxide (TPAOH) molecule not only contains rich carbon atoms, but also well fits to the unit cell of the AlPO-5 framework. Thus, the loading density of TPAOH carbon precursor inside the channels of AlPO-5 crystals is much more than other ones. The resulting SWNTs have higher filling density in the channels and have a better quality than those fabricated using other carbon precursors, as evidenced by the intensive Raman signals in the radial-breathing modes. © 2006 IEEE.