Activator protein-1(AP-1) is an important transcription factor, and dysregulation of its activity has been associated with many human diseases, including various cancers. A novel human gene AC3-33 (GenBank name: c30rf33, Accession No. FLJ31139), which can suppress PMA and Ionomycin induced activation of AP-1, was identified from 650 human func-tion-known genes by using the high throughput-high content cell-based screening technology. The gene whose full cDNA length is 1391 bp containing 6 exons and 5 introns is located in the human chromosome 3q25.31. The predicted protein encoded by this gene contains 251 amino acids with a theoretical molecular weight of 29 kDa. Expression of the AC3-33 gene is widly found in adrenal glands and cervix. The amino acid sequences of AC3-33 is highly conserved, and has no homology to other known proteins. Subcellular localization studies show that the AC3-33 protein was localized in the cytoplasm. Our preliminary results showed that AC3-33 is an important novel gene related to supress AP-1 activity.