Bean yellow mosaic virus (BYMV) is a member of genus Potyvirus within the large and economically important family Potyviridae. During 2010-2012 growing seasons, a BYMV isolate was detected in sunflower fields of Isfahan province (Iran), tentatively designated as BYSun. Virions of BYSun were purified using two cycles of differential centrifugation on 20% and 30% sucrose cushions. SDS-PAGE of purified virus preparations revealed a single protein band with MW of about 33.5 kDa for BYSun. The prepared antiserum against BYSun reacted specifically with infected but not with healthy broad bean sap in serological tests. A 680 bp DNA fragment, corresponding to the partial CI (cylindrical inclusion) region of the viral genome of four selected isolates, was amplified using CIRev/CIFor primers able to detect members of the family Potyviridae. BLAST search showed that the most similar sequence in the databases was that of BYMV-S. Nucleotide sequence identities of BYSun whole genome to those of other BYMV isolates ranged from 75 to 98%. The deduced amino acid sequence of BYSun polyprotein was 85-99% identical to other isolates of BYMV. Phylogenetic analysis of most parts of the genome (especially CP) of different BYMV isolates sequences revealed eight distinct groups including General, Lupin, Monocot, Broad bean, W, Pea, Canna and S. These groups correlated with original natural isolation hosts. BYSun and BYMV-S grouped apart from other isolates, so it was placed within a distinct group called “S”. BYSun is the first isolate of BYMV with fully sequenced genome in Iran.