Gene therapy has become the most effective treatment formonogenic diseases. Congenital LEPTIN deficiency is a rare autosomal recessive monogenic obesity syndrome caused by mutations in the Leptin gene. Ob/ob mouse is a monogenic obesity model, which carries a homozygous point mutation of C to T in Exon 2 of the Leptin gene. Here, we attempted to edit the mutated Leptin gene in ob/ob mice preadipocytes and inguinal adipose tissues using CRISPR/Cas9 to correct theCto Tmutation and restore the production of LEPTIN protein by adipocytes. The edited preadipocytes exhibit a correction of 5.5% of Leptin alleles and produce normal LEPTIN protein when differentiated into mature adipocytes. The ob/ob mice display correction of 1.67% of Leptin alleles, which is sufficient to restore the production and physiological functions of LEPTIN protein, such as suppressing appetite and alleviating insulin resistance. Our study suggests CRISPR/Cas9-mediated in situ genomeediting as a feasible therapeutic strategy for human monogenic diseases, and paves the way for further research on efficient delivery system in potential future clinical application. Copyright (C) 2021, The Authors. Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and Genetics Society of China. Published by Elsevier Limited and Science Press.