We report on the photoluminescence (PL) and lasing characteristics of ZnO nanorod arrays (NRAs) fabricated by hydrothermal process on nanocrystalline ZnO seeded Si and post-growth annealing. The morphology of the ZnO NRAs was examined by field emission scanning electron microscopy and the structure was characterized by x-ray diffraction, Fourier-transform infrared and Raman scattering spectroscopy. The properties of light emission were studied by continuous wave (CW) and 30 ps pulsed ultraviolet excitation. The ZnO NRAs consist of aligned nanorods and are nanocrystalline with wurtzite structure and c-axis orientation. At room temperature, the ZnO NRAs are capable of emitting strong CW PL and pulsed stimulated emission, with the latter showing obvious lasing characteristics. The threshold for lasing was observed to be ~16 kW/cm(2).