The polycomb group (PcG) proteins repress transcription of the target genes and control development by chromatin modification in plants and animals. During vernalization, the Polycomb Repressive Complex 2, containing VERNALIZATION 2 (VRN2), CLF/SWN, FIE, and MSI1, can trimethylate the lysine 27 of histone H3 in the chromtin loci of FLOWER LOCUS C (FLC), the main flowering repressor in Arabidopsis. Therefore, the transcription of FLC is repressed during vernalization and the plant was induced to flowering. Here, we review the machanism of flowering regulation mediated by PcG proteins, which is expected to be valuable to research in vernalization mechanism in cereal.