We reported a novel (-)ssRNA mycovirus isolated from Auricularia heimuer CCMJ1222, using a combination of RNA-seq sequencing, reverse transcription-polymerase chain reaction, 5′ and 3′ rapid amplification of cDNA ends, and Sanger sequencing. Combining database searches, sequence alignment, and phylogenetic analysis, we designated the virus as Auricularia heimuer negative-stranded RNA virus 1 (AhNsRV1). The virus had a monopartite RNA genome related to mymonaviruses (Mononegavirales). The AhNsRV1 genome consists of 11,441 nucleotides and six linear open reading frames (ORFs). The largest ORF encodes a large protein; the second ORF encodes a hypothetical protein, while other ORF functions were unknown. AhNsRV1 was the first (-)ssRNA virus known to infect fungi and was the third virus to be discovered from A. heimuer.