Cr3+-doped ZnO nano-rods with different doping concentrations are prepared via solvothermal method. The doped ZnO nano-rods are characterized by X-ray diffraction and scan electron microscopy, respectively. It was found that no Cr2O3 peaks appeared in the XRD patterns of Cr3+ doped ZnO when the mole ratio of Cr3+/Zn2+ was in the range of 1-10 mol%. The effect of Cr3+ doping on the resistances of the Cr3+-doped ZnO nano-rod sensors was investigated and the results revealed that all Cr3+ did not enter the lattice of ZnO. The amount of Cr3+ had a great influence on the response (Ra/Rg). The sensor based on 3 mot% Cr3+ doped ZnO nano-rods (120 degrees C, 10 h) exhibited high response and good selectivity to trimethylamine, especially, the responses to 0.001 ppm and 0.01 ppm trimethylamine reached 1.2 and 6.8, respectively. The response time and the recovery time for 0.001 ppm trimethylamine were 120 s and 80s, respectively. (C) 2011 Elsevier B.V. All rights reserved.