A recombinant single chain fragment variable (scFv) antibody was constructed from hybridoma cell lines expressing anti-solamargine (As) monoclonal antibody (MAb). The characteristics of the As-scFv protein, expressed in both recombinant Escherichia coli and hairy root, were almost same with those of the original MAb. Up to 220 ng recombinant As-scFv was produced per milligram of soluble protein in transgenic hairy root cultures of S. khasianum. The solasodine glycosides concentration was 2.3 fold higher in the transgenic, than in the wild-type hairy root, reflecting from the soluble As-scFv level. The recombinant S. khasianum plant regenerated from recombinant hairy roots contained 2.3 fold concentration of solasodine glycoside, compared to the regenerated plant from wild-type hairy root. These results suggested that the scFv antibody expressed in transgenic plant controlled the antigen level. This methodology is the first success for molecular breeding of secondary metabolites, without understanding of biosynthetic enzyme.