Previous studies have illustrated that hnRNP K, which could be methylated at arginine residues, plays a key role in coordinating transcriptional responses to DNA damage as a cofactor for p53. In this study, we observed that hnRNP K was markedly arginine methylated in response to UV radiation. Furthermore, arginine methylation of hnRNP K enhanced its affinity with p53. Inhibition of methylation in hnRNP K attenuated the recruitment of p53 to p21 promoter, and reduced p53 transcriptional activity. These data suggested that arginine methylation of hnRNP K is a key element for p53 transcriptional activity.