Abstract: A virus was isolated from cucumber showing mottle mosaic during growing seasons of 2009 and 2010 in Khorasan province of Iran. Based on its serological relationships, biological reactions, Reverse Transcription-Polymerase Chain Reaction (RT-PCR) using specific primers and nucleotide sequence analysis of Coat Protein (CP) gene, the isolated virus was identified as Cucumber Green Mottle Mosaic Virus (CGMMV) and designated as kalat isolate (CGMMV-kalat). Crude sap from infected tissue was mechanically transmitted to various indicator plants which produced characteristic symptoms of tobamovirus infection. However, no symptom was observed in Petunia hybrid, Datura stramonium L., Nicotiana sp. and Cucurbita pepo. In RT-PCR assay with specific primers for detection of CGMMV, a single band of about 490 bp in length was produced from the samples. The amplified DNA was cloned and the nucleotide sequence was determined. Sequence comparisons with the CP gene of other CGMMV isolates present in the GenBank indicated that CGMMV-kalat had high homology with the other isolates (the highest homology could reach 97.9% in nucleic acid level). As well, phylogenetic tree based on CP amino acid sequences was established and the highest amino acid homology was 95.2%. To our knowledge, this is the first report on the occurrence of CGMMV in cucumber in Iran based on biological reactions, RT-PCR and CP gene analyses.