Since the major virulence factor, NSs protein, is an antagonist of IFN responses, the direct attenuation of NSs function may increase host innate immune responses in cells infected with RVFV potentially limiting RVFV replication. Thus, we aimed to attenuate RVFV NSs function(s) by co-expressing nonfunctional NSs. It has been shown that recombinant MP-12 virus encoding truncated NSs at aa.210 to 230 (SAP30-binding domain) does not inhibit IFN-b mRNA synthesis [26] . Thus, we employed a similar strategy to abolish a part of NSs functions by truncating each 17 to 25 aa. Co-expression of such truncated NSs may exhibit dominant-negative phenotype by self-association through the Cterminus at the self-association domain (aa.249 to 265) [65] . In this study, we generated NSs encoding deletions of 17 to 25 amino acids, characterized the functions of truncated NSs, and analyzed the dominant-negative effects of co-expressed truncated NSs in cells infected with RVFV.