Background: Though it is clear that many types of viruses can infect the oral mucosa, its condition for infection is unclear. The purpose of this study was to analyze the conditions for viral infection of normal oral mucosa and explore the possibility of topical gene therapy to oral mucosa using a viral vector. Methods: Freshly taken fragments of the palate and the tongue of mice were used for organ culture. The specimens were exposed to green fluorescent protein (GFP)-adenoviral vector for 1 hour except for the control. Initial viral titer was $6.3{ imes}10^{11};pfu/ml$ and the virus was diluted to working concentrations. The dilution ratio was 1:1,000 ($6.3{ imes}10^8;pfu/ml$), 1:10,000 ($6.3{ imes}10^7;pfu/ml$), and 1:100,000 ($6.3{ imes}10^6;pfu/ml$). They were then cultured on a stainless steel wire mesh in an organ culture dish. The specimens were stereoscopically examined every 24 hours for 6 days, after which they were fixed and analyzed through immunohistochemical methods Results: There was no visible expression in the control, $6.3{ imes}10^6;pfu/ml$, and $6.3{ imes}10^7;pfu/ml$ groups. Initial expression was observed at 24 hours after infection in both the palate and the tongue in $6.3{ imes}10^8;pfu/ml$ and the expression significantly increased until 3 days in the palate and 2 days in the tongue after infection (P<0.05). In both groups, the expression was mostly observed at the resection margin. Immunohistochemical studies showed that the epithelial cells were positive to GFP. Conclusion: The present study showed that topically applied adenovirus containing specific genetic information of GFP could successfully transduce GFP in normal oral epithelial cells at the resection margin in organ culture in terms of dose and exposure time.