Abstract: Transient expression of the GUS gene has been demonstrated in somatic callus of the two varieties of Carica papaya cv. Shahi and Ranchi after co-cultivation with Agrobacterium tumefaciens strain LBA-4404 carrying a binary plastid vector system containing neomycin phosphotransferase gene as the selectable marker and -glucuronidase (GUS) as reporter gene. The mature embryonal axes were used as explants. The co-cultivated explants were transferred into final selection medium containing 500 mg L -1 carbenicillin + 200 mg L -1 cefotaxime + 50 mg L -1 kanamycin. The callus of C. papaya cv. Shahi showed highestGUS activity compared to C. papaya cv. Ranchi. The anatomical section of callus showed the positive GUS activity. All transformed callus grew vigorously in this medium and formed embryos followed by plantlets.