In the cells infected by HSV, various viral proteins are expressed in a cascade style. The expression of immediate-early (IE) gene occurred in early phase of infection is under the control of regulatory elements in upstream sequence of promoter. A series of pCAT expression vectors containing different upstream sequence fragment of α4 - gene, in which relative element is deleted orderly, is constructed and detected in CAT assay. The transcriptional ability of these DNA fragments on α4 - gene are evaluated to investigate their efficacy in early phase infection. The data collected indicated that the expression of IE gene in cells is controlled by various elements in its upstream. Topological distribution of these elements provides probably useful information for further understanding about the mechanism of virus replication.