MicroRNAs are short, noncoding RNAs that play important roles in post-transcriptional regulation. Although many functions of microRNAs in plants and animals have been revealed in recent years, the transcriptional mechanism of microRNA genes is not well understood. To elucidate the transcriptional regulation of microRNA genes, we study and characterize, in a genome scale, the promoters of intergenic microRNA genes in Caenorhabditis elegans, Homo sapiens and Arabidopsis thaliana. Specifically, we show that the known microRNA genes in these species have the same type of promoters as the protein-coding genes. To further characterize the promoters of miRNA genes, we develop a miRNA core promoter prediction method, called common query voting (CoVote). We applied this new method to identify putative core promoters of most known microRNA genes in the three model species of choice.