Most human genetic disease arises from point mutations. These genetic diseases can theoretically be corrected by gene therapy but clinic practice is still far from mature. Nearly half of the pathogenic single-nucleotide polymorphisms (SNPs) are caused by G:C>A:T or T:A>C:G base changes. The best current methods to repair these changes are by base editing without footprint using recently developed CRISPR-Cas9 technology by David Liu’s lab. These base editing methods have been confirmed with precision and efficiency in cultured mammalian cells, but it is barely confirmed and the efficiency is still very low. Animal models are important in dissecting pathogenic mechanism for human genetic diseases and efficacy testing of base correction in vivo. Cytidine base editor BE4 is a newly developed version of cytidine base editing system that converts cytidine (C) to uridine (U) in cultured mammalian cells but has not been proven in vivo. In this study, we have tested this system in cells to inactivate GFP gene and in mice by introducing single-base substitution that leads to a stop codon in tyrosinase gene. High percentage albino coat-colored mice were obtained from black coat-colored donor zygotes after pronuclei microinjection. Sequencing results showed that expected base changes were obtained with high precision and efficiency (56.25%). There are no off-targeting events identified in predicted off-target sites. Results confirm BE4 system can work in vivo with high precision and efficacy, and has great potentials in clinic to repair human genetic mutations.