A cryptic virus, named mulberry cryptic virus 1 (MuCV1), was identified in a mulberry (Morus alba) transcriptome dataset and confirmed using RACE methods. The genome of MuCV1 is composed of two double-stranded RNAs, 1605 bp and 1627 bp in size, encoding an RNA-dependent RNA polymerase (RdRp) and a coat protein (CP), respectively. The 5′-AGAAUU-3′ sequence in the 5′ untranslated region was conserved in the two dsRNAs. Sequence comparisons and phylogenetic analysis based on RdRp and CP sequences both indicated that MuCV1 is a deltapartitivirus (family Partitiviridae).