Temperature dependence of the in-plane conductance of a SmFeAsO0.85 single crystal is measured in c-axis and planar magnetic fields up to 7T. The conductivity near the superconducting transition is well described by two-dimensional (2D) thermal-fluctuation theory. The 2D superconductivity arises as the c-axis coherence length is much shorter than the spacing between neighboring FeAs layers. (c) 2009 Elsevier B.V. All rights reserved.