The sand goby Neogobius pallasi (Berg, 1916) belongs to the family Gobiidae which has a wide distribution in the south of the Caspian Sea basin and its tributaries. The purpose of this study was to determine some of the morphological parameters of sand goby and the appropriate characteristics for the separation of populations in Kaboodval, Zaringol and Shirabad Streams. Both males and females consisted of five age groups (0⁺-4⁺). Seven meristic and 31 distance-based morphometric characters from 104, 30 and 62 specimens were investigated in three streams during the summer in 2008. The comparison of the morphological characteristics among the samples of sand goby showed the significant differences in three Streams (p<0.05), but principal components analysis (PCA) showed that the low characteristics play a role in the population separation. Only the mouth width, lower jaw and upper jaw coefficients were greater than 0.75. It seems that there is more overlap between the samples of Kaboodwal and Zaringol compared to those of Shirabad. This finding is also consistent with their geographic distances