AbstractNovel polyphosphazene nanotubes with closed ends were prepared by polycondensation of HCCP and BPS via an in situ template approach at room temperature. The nanotubes were characterized by FT‐IR and NMR spectroscopy and elemental analysis. Their cross‐linked structures were confirmed. SEM and TEM indicated that they resemble capsicum, with a length of 2–6 µm, and the outer diameters of the two ends were about 200–500 and 100 nm. The majority of nanotubes had inner diameters of about 30–50 nm. The tube ends were closed. TGA analysis showed that their decomposition started at 468 °C. A formation mechanism of the capsicum‐like nanotubes is proposed.magnified image