Pure ZnO and Pd-ZnO nanorod arrays were in-situ grown on the ceramic tube via a simple wet-chemical route. The structural and composition information were examined by means of X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. It is found that the diameters of these nanorods are uniform in the range of 50-200 nm and doping Pd did not change the morphology and diameter. Furthermore, trimethylamine gas sensing properties of these nanorod arrays were systematically investigated. The sensing measured results showed that doping Pd could obviously reduce operating temperature compared to pure ZnO nanorod sensor. Moreover, 1 mol% Pd-doped ZnO nanorod sensor exhibited significantly improved sensing performances to trimethylamine including enhanced response, short response/recovery time, good reproducibility and stability, good selectivity. Meanwhile, the enhanced sensing mechanism of Pd-doped ZnO nanorods was also discussed, which could be explained by the chemical and electronic sensitization theory. Our studies provide a facile in-situ sensing device synthesized route, which could be developed to synthesize other metal oxide sensing device. Moreover, design and formation of Pd-doped ZnO nanorod arrays have potential application for fabricating high performance trimethylamine sensors.