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Optically stimulated luminescence (OSL) dating technique is a reliable method to determine the ages of sand dune sediments. While it seems logical to assume that for these windblown materials (such as sand dune sediments) grains from different sized fractions are suitable for optical dating and would yield identical ages, this was not previously explicitly demonstrated yet. In this study, six samples were selected from the sand dunes intercalated in loess strata near Lanzhou, western Chinese Loess Plateau, and different grain-size quartz fractions (e.g. 38-63 mu m, 90-150 mu m, 150-200 mu m, 200-250 mu m and 250-300 mu m) were extracted to compare the OSL ages of different grain-size quartz. The results show that: (1) quartz OSL ages derived from different grain-size fractions produce identical ages within errors, confirming that the ages resulting from both coarse silt-sized (or middle grain of 38-63 mu m) and sand-sized (90-300 mu m) quartz can represent the periods of sand dune accumulation; (2) the OSL ages of the selected sand dune samples fall into ca. 28-18 ka, suggesting that the sand dune accumulation occurred during the marine isotope stage 2 (MIS 2) in current study area, which might imply regional increased aridity on the western Chinese Loess Plateau. (C) 2011 Elsevier BM. All rights reserved.