Complementary sense promoter from cotton leaf curl virus (CLCuV) is a novel plant promoter for genetic engineering that could drive high-level foreign gene expression in plant. To determine the optimal promoter sequence for gene expression, CLCuV promoter was deleted from its 5' end to form promoter fragments with five different lengths, and chimeric gus genes were constructed using the promoter deletion. These vectors were delivered into Agrobacterium and tobacco (Nicotiana tabacum L. cv. Xanthi) plants which were transformed by leaf discs method. GUS activity of transgenic plants was measured. The results showed that GUS activities with the promoter deleted to -287 and -271 from the translation initiation site were respectively about five and three times that of full-length promoter. There exists a cis-element which is important for the expressing activity in phloem from -271 to -176. Deletion from -176 to -141 resulted in a 20-30-fold reduction in GUS activity in leaves with weak activity in leaves and stems and losing GUS activity in roots. The functional domains of complementary sense gene promoter of CLCuV were firstly analyzed and compared. It was found that the promoter activity with the deletion of negative cis-elements was much stronger than that of full-length promoter and was about twelve times on average that of CaMV 35S promoter, suggesting that the promoter has great application potential. Results also provide novel clues for understanding the mechanisms of geminivirus gene regulation and interaction between virus and plant.