Abstract: Rhamnosyltransferase (SGT3) is a key enzyme involved in synthesis of plant glycoalkaloids, and mainly catalyzes the transformation of α-solanine and α-chaconine from their β-form. We studied the SGT3 gene expression and its promoter function in potato cultivars (Solanum tuberosum), and found that after 24 hours red light treatment, the transcriptional expression of SGT3 was increased 26.8 fold compared with control (under dark). The data thus suggested that red light induced the expression of SGT3. To further understand the regulation mechanism of SGT3, the putative SGT3 promoter region (2449 bp upstream of the open reading frame) was cloned and the sequence was analyzed to predict the cis-elements including promoter core sequences, enhancer sequences, inhibiting sequences, pathogen- responsive element, drought- and ABA- responsive element, and a few light-regulated elements. The transcription start site of the promoter is located 152 bp upstream of the translation start site. To study the function of the SGT3 promoter, the GUS expression vector driven by SGT3 or CMV 35S promoter were constructed and transformed to tobacco leaves to analyze the transient expression and stable expression. The results demonstrated that the SGT3 promoter can drive the expression of GUS, but the expression level was less than that driven by the CMV 35S promoter. The highest GUS expression was detected in tobacco leaves transformed by P572 and P979 but the GUS expression was decreased with P1312 and P1870. More positive regulatory elements were observed within 1000 bp upstream of the start code. The tissue specificity analysis indicated that the SGT3 driven GUS expression was mainly concentrated in the veins of the tobacco leaves, but was not detected in mesophyll cells. In the root, GUS was detected in meristem and vascular tissues. In the stem, GUS was detected in epidermis, xylem and phloem of tobacco stems.