GUS reporter expression from 11 basal promoters (CaMV –90) with G-box cores (CACGTG) was analysed to evaluate the regulatory roles of G-box flanking sequences. While most G-box motifs exhibited some tissue preference of gene expression, a distinct tissue-specific expression was not apparent. However, one of 11 G-box sequences, the G-box 10 (GCCACGTGCC) tetramer, conferred a high-level constitutive expression in seed, root, leaf, axillary bud, almost all parts of flower buds and pollen of transgenic tobacco plants. Furthermore, the G-box 10 tetramer promoter exhibited high-level expression in transgenic dicot carrot and monocot rice. This is apparently the first report of a G-box motif conferring a high-level constitutive expression in a non-tissue-specific manner.