In the post-genomic era, identifying and characterizing various DNA-protein interactions are a major challenge in the research of gene transcriptional regulation. Although many techniques can be used for this purpose, chromatin immunoprecipitation assay (ChIP), by contrast, is ideally suited for studying DNA-protein interactions in vivo. In recent years, standard ChIP assay has been modified to uncover some known factors' unknown target sequences, especially when combined with DNA microarray and molecular cloning strategies. These high-throughput ChIP assays are more and more used to reveal the distribution profile of trans-acting factor binding sites throughout the genome, which may yield many new insights into the DNA-protein interaction network. This article summarized the methods of ChIP assay, and highlighted recent progress in the application of this technique.