Dnop5 is a member of the conserved nop5/sik1 gene family, which encode components of small nucleolar ribonucleoprotein( snoRNP) complexes. To study the function of DNop5, we generated the polyclonal antibody and determined its expression pattern. It is highly expressed in different periods of the Drosophila development. We used heritable RNA interference (RNAi) in combination with the yeast GAL4/UAS binary system to knock down the DNop5 protein. It resulted in lethality and dramatic somatic anomalies in RNAi mutant fly, in which the DNop5 protein is reduced efficiently. Northern blotting showed that the processing of 18S rRNA was disrupted in DNop5 knock down fly, but 28S rRNA is normal. These results suggest that DNop5 is essential for the Drosophila growth and function in the execution of early pre-rRNA processing steps that lead to formation of 18S rRNA.