Inulins are nano-meter size semi-crystalline particles, composed of oligomeric fructose units. This bio-macromolecular material has been subjected to fine micro-structural analysis under temperature variations using mainly positron annihilation spectroscopy for the first time. The results show a non-monotonous temperature sensitive behavior of the positron parameters that help to understand the molecular stacking pattern. Considerable variation of its free volume size has been observed through the ortho-positronium pick-off component annihilation results. The material shows a major thermotropic transition at similar to 320 K and further a structure loss due to glass transition. Differential Scanning Calorimetry confirms the onset of the major molecular transition around the same temperature with an enthalpy change of Delta H similar to 379 J/gm and thermo-gravimetric analysis shows a similar to 7.5% mass loss in the said transition. (C) 2015 Elsevier Ltd. All rights reserved.