A novel double-stranded RNA (dsRNA) mycovirus, named "Fusarium incarnatum alternavirus 1" (FiAV1), was found in Fusarium incarnatum strain LY003-07, the causal agent of peony root rot. The complete genome of FiAV1 is composed of three dsRNA segments, dsRNA1 (3548 nt), dsRNA2 (2514 nt), and dsRNA3 (2498 nt), with one open reading frame on each of their positive-sense strands. As found in other viruses of the proposed family Alternaviridae, the positive-sense strand of each genomic dsRNA of FiAV1 has a poly(A) tail and the 5′-terminal nonamer sequence 5′-GGCTGTGTG-3′. Based on a multiple sequence alignment and phylogenetic analysis based on the RdRps amino acid sequence, FiAV1 is suggested to be a new strain of a potential new species, for which the name "Fusarium alternavirus 1" is proposed, that includes Fusarium poae alternavirus 1 (FpAV1) and Fusarium graminearum alternavirus 1 (FgAV1/AH11) of the proposed family "Alternaviridae". This is the first report of a mycovirus of the proposed family "Alternaviridae" that infects F. incarnatum.