La2CuO4 nanofibers (ca. 30 nm in diameter and 3 mu m in length) have been grown in situ by using single walled carbon nanotubes (SWNTs; ca. 2 nm in inner diameter; made via cracking CH4 over the catalyst Of Mg0.8Mo0.05Ni0.10Co0.05Ox at 800 degrees C) as templates under mild hydrothermal conditions and a temperature around 60 degrees C. During synthesis, the surfactant poly(ethylene glycol)-block-poly(propylene glycol) block-poly(ethylene glycol) and H2O2 were added to disperse SWNTs and oxidize the reactants, respectively. The structure of La2CuO4 nanofibers was confirmed by powder X-ray diffraction (XRD) and their morphologies were observed with field emission scanning electron microscope (FESEM) at the hydrothermal synthesis lasting for 5, 20 and 40 h, respectively. The La2CuO4 crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. Twenty hours is an optimum reaction time to obtain regular crystal fibers. The La2CuO4 nanofibers are probably cubic rather than round and may capsulate SWNTs. (C) 2006 Elsevier Inc. All rights reserved.