To investigate the molecular characteristics, interaction, and nutritional regulation of CDK2 in grass carp (Ctenopharyngodon idella), we obtained the grass carp cdk2 sequence by cloning; its open reading frame is 897 bp, encoding 298 amino acids. It exhibited a high degree of sequence and structure conservation in the analyzed species. The results of codon bias and cluster analyses based on CDK2 suggested that the grass carp has the closest relationship with zebrafish. Compared with clustering based on cdk2 RSCU, a phylogenetic tree analysis based on CDK2 sequence was more consistent with the conventional species classification. Tissue expression analysis showed the highest cdk2 mRNA levels in blood (P＜0.05), liver, and spleen; molecular docking and yeast two-hybrid assays were employed to analyze the interaction between grass carp CDK2 and its downstream phosphorylated substrate protein CDX2. The results showed that grass carp CDK2 interacted with CDK2. Furthermore, the regulation of different inclusion levels of free amino acid CAA (free amino acids: lys and glu), dipeptide KE (lys-glu, KE), tripeptide GHK (gly-his-glu, GHK) on cdk2 expression were examined, and the results revealed that compared with the control and other treatment groups, cdk2 expression showed the highest expression in the 0.5% GHK group; cdk2 expression of the CAA groups was higher than those of the KE dipeptide group which showed similar amino acids as the CAA group. In summary, cdk2 expression in grass carp exhibits tissue specificity; CDK2 interacted with CDX2; and its expression was regulated by the inclusion level of amino acids and oligopeptides. This study provides new clues for studying the molecular characteristics of grass carp cdk2 exploring the regulatory mechanism of intestinal function in other teleost fish, and provides a theoretical basis for further study on the molecular regulating mechanism of cdk2 on transporting and absorption of amino acids and oligopeptides.