Objective: Viral interference has been demonstrated in different systems, such as the effect of enterovirus infection on live-attenuated oral polio vaccine. In this study, the effect of reovirus which could exist in the human intestinal tract on poliovirus vaccine strains was investigated and could be an important factor to consider in oral polio vaccination. Methods: Cells were infected with reovirus, then superinfected with poliovirus. The amount of viral yields was measured by the TCID₅₀ and plaque assay methods. Polioviral RNA synthesis was studied by real-time RT-PCR and the viral RNA load was calculated. Viral protein synthesis was determined using the techniques of immunoflourescent staining and PAGE followed by the immunoblotting experiment. Results: Poliovirus superinfection of reovirus-infected cells resulted in inhibition of poliovirus replication. It was found that the inhibitory effect of reovirus was after establishment of its infection (2 h postinfection). There was no competition between the two viruses for cell attachment but poliovirus RNA and protein synthesis were inhibited. Conclusion: Infection of cells with reovirus could interfere with the growth of poliovirus upon superinfection. This phenomenon could be important to consider when using attenuated poliovirus vaccine.