Since smallpox vaccination was discontinued in 1980, there has been a resurgence of poxvirus infections, particularly the monkeypox virus. Without a global recommendation to use the smallpox vaccine, the population is not immune, posing a severe threat to public health. Given these circumstances, it is crucial to understand the relationship between poxviruses and their hosts. Therefore, this study focuses on the ectromelia virus, the causative agent of mousepox, which serves as an excellent model for studying poxvirus pathogenesis. Additionally, we investigated the role of mitochondria in innate antiviral immunity during ECTV infection, focusing specifically on mitochondrial antiviral signaling protein. The study used a Moscow strain of ECTV and L929 mouse fibroblasts. Cells were treated with ECTV and chemical modulators of mitochondrial network: Mdivi-1 and CCCP. Our investigation revealed that an elongated mitochondrial network attenuates the suppression of MAVS-dependent immunity by ECTV and reduces ECTV replication in L929 fibroblasts compared to cells with an unaltered mitochondrial network. Conversely, a fragmented mitochondrial network reduces the number of progeny virions while increasing the inhibition of the virus-induced immune response during infection. In conclusion, our study showed that modifications of mitochondrial network morphology alter MAVS-dependent immunity in ECTV-infected mouse L929 fibroblasts.