Obesity has become a severe public health problem across the world, and seriously affects the health and life quality of human beings. Here we generated lepr and mc4r mutant zebrafish via the CRISPR/Cas9 technique, and performed morphological and functional characterizations of those mutants. We observed that there was no significant phenotypic difference between homozygous mutants and wild-type controls before 2.5 months post-fertilization (mpf). However, the adult lepr-/- and mc4r-/- individuals displayed increased food intake, heavier weight, and higher body fat percentage, the characteristics of obesity phenotypes. Blood glucose test showed that overfeeding induced significantly impaired glucose tolerance in adult lepr-/- and mc4r-/- zebrafish. Furthermore, we analyzed 76 energy metabolism-related transcripts in lepr-/- and mc4r-/- zebrafish livers by using real-time RT-PCR, and compared the results with the published microarray data of Lepob/ob mouse livers, and found that the changes in the expression of insulin/IGF signaling (IIS) pathway genes in lepr-/- zebrafish and Lepob/ob mouse were positively correlated, suggesting that the IIS pathway maintains functional conservation between zebrafish and mammals during the evolution of the obesity-regulating molecule network.