Abstract: To investigate effects of high energy diets on serum biochemical indices of grass carp (Ctenopharyngodon idella), grass carp N= 320, average initial body weight=(55.0±2.5) g were randomly assigned into 4 groups with 4 replicates for each group (N=20 fish/replicate) to fed three times daily to satiation with the control diet (CON) and three high energy diets for 11 weeks. The 3 high energy diets were 11% increased protein, 11% increased fat or 11% increased Carbohydrate compared to the control diet, respectively. The fish were fasted for 48h and then refed a single meal for 0, 2, 8, or 24 hours before collection for analyzing eight serum biochemical indices. Statistical analysis using two-way ANOVA showed that seven serum biochemical indices except total cholesterol (TCHO) were significantly affected by refeeding time, and all 8 biochemical indices were significantly affected by the different diets. Peak values of glucose (GLU) contents and aspartate transaminase (AST) activities presented at 2h after refeeding, and peak values of alanine transaminase (ALT), alkaline phosphatase (ALP) activities and low density lipoprotein-cholesterol (LDLC) contents appeared at 24h after refeeding. The peak value of triacylglycerol (TAG) content occurred at 8h after refeeding, but there was no obvious peak value for serum TCHO or high density lipoprotein-cholesterol (HDLC) contents. At 24h after refeeding, compared with the CON diet, the higher energy diets had higher GLU contents and ALT activities but with similar activities of AST and ALP, and the contents of TAG, TCHO and HDLC. Our results demonstrated that both refeeding time and high energy diets regulated the serum biochemical indices, indicating that it is necessary to make sampling time synchronize in different groups for the accuracy of serum biochemical indices.