Stability of ribosomal RNA (rRNA) is not only essential for ribosome biogenesis but also crucial to the maintenance of proper translational level for cell viability. rRNA processing (maturation) is one of the key steps to derive functional rRNA, and to date, a large number of factors involved in this process have been identified. We investigated Rps0 binding proteins in fission yeast, Schizosaccharomyces pombe, and revealed that Rps0p is associated with Rps21 protein, similar to that of our previous observation in human cells. We demonstrated that both rps0(+)s and rps21(+) are essential genes for S. pombe analyzed by tetrad dissection assay. To study the functions of both genes, we established disruption strains transformed with inducible rescue plasmids. Using the strains our studies revealed that the loss of rps0(+)s or rps21(+) led to a deficiency of 40S ribosomal subunit formation. Additional functional studies indicate that this phenomenon is likely to be caused by insufficient 18S rRNA stability. The possible role of Rps0p and Rps21 that contribute to 18S rRNA maturation is further discussed.