The present invention relates to a cytosol-penetrating antibody and a use thereof, and specifically, to a light chain variable region and/or heavy chain variable region positioned in a cytosol, a cytosol-penetrating antibody containing same, a method for producing same, and a use thereof, wherein the light chain variable region and/or heavy chain variable region exhibit notably enhanced endosomal escape efficiency as a result of an investigation of a structural mechanism for inducing endosomal escape which is the escape from an endosome to a cytosol after cellular internalization through a membrane protein of a cell membrane of a living cell.
