Conventional antibodies are unstable, aggregate, and do not work inside cells. We succeeded in developing a versatile method for creating a fully functional cytoplasmic antibody (named STAND), which does not aggregate in the intracellular environment and can approach intracellular disease therapeutic targets. Antibodies (single-chain Fv: scFv, variable domain of heavy chain of heavy chain antibody: VHH) are stabilized by fusing stabilizer peptide tags.