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Thirty eight ecotypes of watermelon were collected from different parts of Iran. After the preparation of the field, these eotypes were cultivated in a completely randomized block design with three replications. In order to invest-igate genetic diversity, genomic DNA samples were extracted from leaves and Polymerase chain reactions were optimized using 14 SRAP primer pairs. One hundred thirty six polymorphic bands were detected, of which the EM10-Me4 was the most abundant primer pair with 19 bands and EM16-Me4 and EM16-Me14 were the least primer pairs with 7 bands. PIC index varied from 0.20 to 0.32 and genetic diversity was 0.17 to 0.28 on the basis of Nei index. Fisher's Linear Detection Analysis showed that the UPGMA method and the grouping accuracy of about 90% are more appropriate than other cluster analysis methods. Cluster analysis, using Jakard method, was performed and the ecotypes studied were classified into five distinct groups. Based on the PCA, the first and second components included 92.5% of the variation, which represents the proper distribution of the markers on the whole genome.