A glucose-inducible gene in S. pombe is rrg1+. Its mRNA level is rapidly decreased and increased by glucose-depletion and readdition, respectively. The previous study revealed that the rrg1+ expression was regulated by glucose-dependent mRNA stability control. To understand the significance of the glucose-dependent expression of rrg1+, the cellular function of rrg1+ was explored. Deletion of the rrg1+ gene from the haploid chromosome of S. pombe cells did not lead to cell lethality but brought about cell size reduction, which was accompanied by fast cell proliferation. In accordance with this result, the overexpression of the Rrgl protein under the control of the nmt1 promoter produced elongated cells of G2 delay, and consequently resulted in the slowing-down of cell proliferation. In addition, the rrg1+ mRNA level showed cell-cycle dependent changes, peaking at G2/M. These results demonstrate that Rrg1 might be involved in the negative regulation of cell proliferation and G2/M progression for cell size control.