Cotton leaf curl virus (CLCuV) is a type of single-stranded DMA virus, belonging to geminivirus of subgroup Ⅲ. In order to determine the function of CLCuV large intergenic region (LIR), total DNA of CLCuV-infected cotton leaves was used as template, and fragment of LIR was obtained by PCR and inserted into clone vector. The fragment of LIR was fused with gus reporter gene and nos terminator in the orientation of transcription of virion sense and complementary sense respectively, and the plant expression vectors were constructed. GUS activity of Agrobacte-rium-mediated transgenic tobacco was measured. The result indicated that LIR showed strong promoter activity in complementary sense gene orientation. Average GUS activity of the complementary sense promoter was 5-6 times that of CaMV 35S promoter, and the highest GUS activity of individual plant was ten times of that of CaMV 35S promoter. Histochemical localization confirmed its activity in both mesophyll and vascular tissues. Activity of virion sense o Cotton leaf curl virus (CLCuV) is a type of single-stranded DMA virus, belonging to geminivirus of subgroup III. In order to determine the function of CLCuV large intergenic region (LIR), total DNA of CLCuV-infected cotton leaves was used as The fragment of LIR was fused with gus reporter gene and nos terminator in the orientation of transcription of virion sense and complementary sense respectively, and the plant expression vectors were constructed. GUS activity of Agrobacte-rium-mediated transgenic tobacco was measured. The result indicated that LIR showed strong promoter activity in complementary sense gene orientation. Average GUS activity of the complementary sense promoter was 5-6 times that of CaMV 35S promoter, and the highest GUS activity of individual plant was ten times of that of CaMV 35S promoter. Histochemical localization confirmed its activity in both mesophyll and vascular tissues. ty of virion sense o