Wolbachia, a vertically transmitted intracellular bacterium, is known to disrupt the reproductive biology of its insect hosts. However, in *Drosophila melanogaster*, the strong and consistent effects of Wolbachia infection have not been documented. This study reports that Wolbachia infection in *D. melanogaster* increases resistance to the RNA virus *Drosophila C virus* (DCV), reducing viral loads in infected flies. The bacteria identified as inducing this resistance are Wolbachia. Additionally, Wolbachia also enhances resistance to two other RNA viruses (*Nora virus* and *Flock House virus*) but not to a DNA virus (*Insect Iridescence Virus 6*). These findings identify a new major factor regulating *D. melanogaster* resistance to RNA viruses and suggest that the response of hosts to pathogens can be modulated by interactions with other microorganisms. This is the first report of a strong beneficial effect of Wolbachia infection in *D. melanogaster*, which may explain the prevalence of Wolbachia in natural populations.Wolbachia, a vertically transmitted intracellular bacterium, is known to disrupt the reproductive biology of its insect hosts. However, in *Drosophila melanogaster*, the strong and consistent effects of Wolbachia infection have not been documented. This study reports that Wolbachia infection in *D. melanogaster* increases resistance to the RNA virus *Drosophila C virus* (DCV), reducing viral loads in infected flies. The bacteria identified as inducing this resistance are Wolbachia. Additionally, Wolbachia also enhances resistance to two other RNA viruses (*Nora virus* and *Flock House virus*) but not to a DNA virus (*Insect Iridescence Virus 6*). These findings identify a new major factor regulating *D. melanogaster* resistance to RNA viruses and suggest that the response of hosts to pathogens can be modulated by interactions with other microorganisms. This is the first report of a strong beneficial effect of Wolbachia infection in *D. melanogaster*, which may explain the prevalence of Wolbachia in natural populations.