ZnO nanorods were prepared on the silicon (100) substrates using the chemical solution deposition method (CBD) without catalyst under a low temperature (90Β°C). The cool water was used to dissolve the mixture of zinc nitrate hexahydrate (Zn (NO 3 ) 2 β’6H 2 O) and methenamine (C 6 H 12 N 4 ) in order to decrease the size of ZnO nanorods. From the X-ray diffraction (XRD) results, it can be seen that the growth orientation of the asprepared ZnO nanorods was (002). Scanning electron microscopy (SEM) results illustrated that the nanorods had a hexagonal wurzite structure and average diameter of about 120nm. The average diameter of nanorods prepared by the cool water process was much smaller than that by the room-temperature (RT) water process we always used. Photoluminescence (PL) measurements were also carried out. The result showed that a blue shift in UV emission band appeared in the PL spectrum of the sample grown with cool water process, which was mainly due to the reduction of tensile strain when the diameter of the ZnO nanorods decreased.