In order to investigate the morphological, biological and genetically relatedness of different populations of Root Knot Nematode on pistachio, during 2004, 93 populations were collected from infected roots and related soil. These populations were obtained from different regions of Kerman province on different pistachio cultivars such as Fandoghi, Akbari, Ahmad aghaie, kale-ghouchee and Badami. Purification and multiplication of each population were done on two tomato cultivars, Rutgers and Cormello. Total DNA was extracted from eggs of all populations and two species of Root Knot Nematode; Meloidogyne javanica and M. incognita were identified using species-specific primers .The most cosmopolitan and widespread species was M. javanica with 88 percent of whole collected populations. Morphological and morphometerical characteristics of perineal pattern in M. javanica populations revealed high variation among them. Based on analysis of morphological (qualitative) characteristics 22 to 100 percent similarity was estimated among M. javanica populations. Analysis of morphometerical (quantitative) characteristics also confirmed this high level of variation between different populations of M. javanica . M. incognita was limitedly dispersed in pistachio growing areas of Kerman province. Perineal pattern of this species also lead to find a high level of variations. Based on analysis of qualitative morphological characteristics 15-100 percent similarity was estimated among different M. incognita populations. The analysis of morphometerical characteristics also confirmed this variation among different M. incognita populations. Biological variation among these two species populations were also checked using host differential test based on Saser and Carter method. All M. javanica populations could form galls on tobacco, watermelon and tomato. But the gall formation ability on pepper was variable and 48 percent of M. javanica populations could form gall on pepper. This is the first report of Pepper successful parasitism by M. javanica in Iran . M. incognita populations also showed different interactions with differential hosts. IN4 population could have a successful parasitism and form galls on pepper, watermelon and tomato. This population identified as Race 1 of M. incognita. This is the first report of Race 1 of M. incognita on pistachio in Iran . IN89 population couldn’t form galls on co