Leaf spot disease is known as one of the limiting factors in cucumber cultivation in east Azarbaijan province and causes major damages on the crop yield annually. Purpose of the current study was to monitor leaf spot disease of cucumber in East Azerbaijan province and identify the pathogenic fungal species using morphological data. To this purpose, sampling was carried out during summer 2013 from main cucumber production areas of Shabestar, Ahar, Myianeh and Basmenj regians. During this research, a total of 90 samples were collected and 100 fungal isolates were isolated from infected samples that had various symptoms of leaf spot. Results of the present study confirmed that the leaf spot symptoms were caused by different fungal species in the provincial farms. By morphological study and investigation of macroscopic and microscopic features, the fungal species of Stemphylium mali, Ulocladium atrum, Cladosporium sp., Nigrospora oryzae, Bipolaris sorkiniana, Phoma sp., Pseudoprenospora CUBENSIS, Bipolaris spicifera, Curvularia sp., Alternaria tenuissima were identified as the causal agent of cucumber leaf spot disease. Among the identified species, isolates of Alternaria tenuissima and Pseudoprenospora CUBENSIS were more frequent than others with 48% and 13% isolation frequencies, respectively.