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Sixty-two surface soil samples, collected along a precipitation gradient in the Loess Plateau and the Alxa Plateau area, northwest China, were analyzed using environmental magnetic parameters (chi(lf), chi(fd)%, chi(ARM), SIRM, HIRM, SOFT, and back field IRM), grain size, and weight loss on ignition. The results show that the magnetic mineral assemblage in the surface soil is dominated by magnetite and maghemite, with some hematite. Cross plots of chi(fd)% vs. chi(ARM)/SIRM indicate that the main magnetic grain sizes in the surface soils are pseudo single domain (PSD) and multidomain (MD). The samples from the Alxa area are dominated by magnetic minerals with a larger grain size while those from the Loess Plateau are dominated by magnetic minerals with a finer grain size. The main magnetic minerals in the surface soil of the Loess Plateau originate from both the aeolian dust and pedogenic processes, with the later dominating. Compared to magnetic susceptibility, frequency-dependent magnetic susceptibility has a stronger correlation with precipitation in this large area of complex geology and topography. This result is not consistent with previous studies and we suggest that caution is needed when using magnetic susceptibility as an indicator of environmental change in arid regions. (C) 2011 Elsevier Ltd. All rights reserved.