The phase conversions and morphological changes of commercial alumina nanofibers (ANF) with 7 and 40 nm in diameter during heat treatment were investigated. These super-high aspect ratio (length-to-diameter ratio is similar to 10(7)) fibers are mostly composed of partially hydrated (2-6 wt.%) gamma-alumina phase. The transformations of the ANF during heating up to 1480 degrees C were studied simultaneous coupled thermal analysis (TG-DSC-FTIR) supported by XRD and SEM examinations. It was found that for ANF gamma-phase starts to transform into stable alpha-alumina from similar to 1250 degrees C, but the water releases during most of the heating time at least in two stages. The behavior of the material and observed changes are discussed and compared with literature date for different alumina materials. (C) 2013 Elsevier B.V. All rights reserved.