During 2017-2018 growing season, some fields of cucurbits in Iran (North and northeast) were surveyed for the presence of Watermelon mosaic virus (WMV) and other common cucurbit viruses. RNA extractions from symptomatic leaf samples were tested by RT-PCR using two degenerate primer pairs (CIF/Rev and NIb2F/3R) targeting the two separated partial regions of the Potyvirus genome (CI and NIb respectively); only 5 out of 10 samples were confirmed to be infected with WMV. To verify molecular variability, 5 WMV isolates were cloned and then sequenced. Comparison of the partial CI and NIb genes sequences showed 94.55-99.14% nucleotide identity among isolates, whereas the amino acid identity was 98.71- 100% respectively, suggesting selection for amino acid conservation. Phylogenetic tree based on CI revealed the separation of WMV isolates into two major divergent evolutionary lineages. Phylogenetic analyses grouped Iranian WMV isolates together with isolates from France, Italy, Spain, Turkey, South Korea, and the US in group I. Analysis of the NIb partial sequence showed nucleotide and amino acid identity from 94.83 to 100% and 97.25 to 100% respectively. Phylogenetic analysis based on NIb placed all the studied isolates in one group where most of the world WMV isolates were exist. Biological results showed Iranian WMV isolates infect C. melo, C. lanatus, C. moschata and C. sativus causing mild mosaic symptoms on the leaves. Whereas, C. pepo plant demonstrated mild to severe mosaic and malformation symptoms on the leaves

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