Beet curly top virus (BCTV) is a member of the genus Curtovirus and the Geminiviridae family that causing disease on plants such as sugar beet, bean and pepper. Also bean, affected by other viruses such as Cucumber mosaic virus (CMV). On the other hand, both viruses have a very wide host range, there is a possibility of simultaneous infection of these two viruses in different hosts. According to the published results that the simultaneous infection of some viruses increases the severity of damage, because of this the effect of simultaneous infection of BCTV and CMV on Akhtar cultivar, which previously its resistance to Iranian isolates of Beet curly top virus has been shown, as well as the Goli cultivar with unknown resistance were evaluated. The experiment was conducted in a completely randomized design with six treatments, first BCTV and then CMV, first CMV and then BCTV, simultaneous and single infection of both viruses and control treatment. The results of this experiment showed that in the simultaneous infection, the symptoms of leaf curl and dwarfing was enhanced and symptoms of yellow vein also was observed, while in single-infection of viruses, appeared less leaf curl and dwarf symptoms. The results of fresh and dry weights and leaf number of plants showed that simultaneous treatments had a lower mean number of treatments than with single infection of both viruses. The data obtained from the semi-quantitative PCR showed that simultaneous treatments, in addition to detection one week earlier than single treatments they also had a higher concentration of BCTV, which suggests, BCTV has been more replicated in the presence of CMV and also there is a synergistic interaction between these two viruses. But the results of experiment on Goli cultivar were different, such that, the typical symptoms of disease even in simultaneous treatments were not observed. Consequently, probably this cultivar can be introduced as resistant cultivar versus curly top virus.