Several members of the Schlafen (SLFN) protein family exhibit antiviral activity through distinct molecular mechanisms. SLFN11 and SLFN13 restrict HIV-1 infection by degrading specific subsets of tRNAs, thereby impairing translation of viral mRNAs enriched in rare codons. Notably, SLFN11, but not SLFN13, inhibits West Nile virus (WNV) replication. Cells lacking SLFN11 are more permissive to WNV infection, and the virions produced in these cells display increased infectivity. Because SLFN11 and SLFN13 are expressed in humans but absent in mice, in vivo studies of their antiviral roles have been limited. Two murine Schlafen proteins, SLFN8 and SLFN9, which originated through gene duplication, have been proposed as the functional counterparts of human SLFN11 and SLFN13. To investigate this relationship, we examined the ability of SLFN8 and SLFN9 to inhibit WNV replication. Human A172 cells, highly permissive to WNV infection, were engineered to lack SLFN11 and to stably express either murine SLFN8 or SLFN9. Following WNV infection, viral replication and virion production were quantified by plaque assay and RT-qPCR, respectively. Our results demonstrate that SLFN8, but not SLFN9, reduces WNV infection, indicating that SLFN8 functions as the murine ortholog of human SLFN11.