Plants of the species Gomphocarpus physocarpus, commonly known as balloon plant or swan plant, exhibiting virus-like symptoms of mosaic, mottle and crinkling were observed and collected in the southwestern part of Taiwan in 2015. Electron microscopic examination showed the presence of virus-like flexuous-rod particles. Potyvirus pinwheel-shape and laminated inclusion bodies were observed in the preparations of ultrathin sections of diseased leaves. The complete genome sequence of the potyvirus of balloon plant was determined. It is 9998 nucleotides in length, excluding the 3'-terminal poly(A) tail. It contains two open reading frames encoding a polyprotein of 3196 amino acids and a PIPO protein of 89 amino acids. The polyprotein gene shares 52.8-68.4% nucleotide sequence identity and 40.2-75.8% amino acid sequence identity with other potyviruses tested. Molecular analysis indicates that the virus is most closely related to but distinct from keunjorong mosaic virus (KjMV). The virus causing mosaic, mottle and crinkling on Gomphocarpus plants (gomphocarpus mosaic virus, GoMV) likely belongs to a new species of the genus Potyvirus.