Dicer proteins are ribonuclease III enzymes that process double stranded RNA precursors into small RNAs categorized as small interfering RNAs (siRNAs) or microRNAs (miRNAs), which suppress gene expression through the RNA silencing mechanism. We have isolated a dicer-like gene (dcl-1) of Mucor circinelloides, the first gene of this family to be identified in zygomycetes. The dcl-1 mRNA occurred in multiple forms, including the truncated molecules that result from premature polyadenylation. Null dcl-1 mutants were not impaired as regards transgene-induced gene silencing, since they exhibited the same silencing frequency as the wild-type strain and accumulated the two size classes of siRNA associated with RNA silencing in M. circinelloides. However, dcl-1 mutants showed a reduced growth rate and a hyphal growth alteration, which suggests that the dcl-1 gene has some role in the control of endogenous functions.