The present invention relates to a method for inhibiting intracellularly activated RAS using an antibody having cytoplasmic penetration ability in the form of a complete immunoglobulin. The present invention also relates to a method for modulating the activity of a heavy chain variable region (VH) that induces a complete immunoglobulin type antibody to actively infiltrate the cytoplasm of living cells into the cytoplasmically activated RAS by intracellularization and endosome excretion, And antibodies comprising the same. The present invention also relates to a method for inhibiting the growth of cancer or tumor cells using the antibody, and a method for treating cancer or tumor. The present invention also relates to a screening method for a heavy chain variable region that specifically binds to cytoplasmic RAS. The present invention also relates to biologically active molecules selected from the group consisting of peptides, proteins, small molecule drugs, nanoparticles and liposomes fused to the antibody. The present invention also relates to a composition for the prevention, treatment or diagnosis of cancer, which comprises a biologically active molecule selected from the group consisting of the above antibody, peptide, protein, small molecule drug, nanoparticle and liposome fused thereto. The invention also relates to the light chain variable region and a polynucleotide encoding the antibody. The method of inhibiting intracellularly activated RAS using an immunoglobulin-type antibody having cytoplasmic penetration ability provided by the present invention is characterized in that the antibody penetrates into a living cell and the activated (GTP) Binding RAS) is capable of targeting and activating an activated (GTP bound) RAS located in the cytoplasm of a living cell inner cell. In addition, the light chain variable region of the antibody of the present invention or the antibody comprising the same may penetrate into living cells without special external protein
