The evolutionary conserved CCR4-NOT multi subunit complex is involved in different aspects of mRNA metabolism, including mRNA synthesis initiation and mRNA deadenylation (shortening of the poly(A) tail) in yeast and higher eukaryotes. Here we report the characterization of the gene encoding the Caf1 subunit of this complex in Caenorhabditis elegans, ccf-1, and the phenotypes associated with its inactivation. Use of staged populations and of mutants strains with altered germline showed that ccf-1 is predominantly expressed in embryos and adults. Loss of ccf-1 function, by both RNAi and a deletion allele, caused early embryonic and larval lethality. It also resulted in sterility in both males and hermaphrodites by blocking germ cell development at the pachytene stage of meiosis I. These results reveal that ccf-1 is an essential factor for both somatic and germline development in C. elegans. Functional analysis of ccf-1 may contribute to the understanding of the molecular role of the CCR4-NOT complex.