Medicinal plants historically have always had a special affinity with human beings and their medicinal effects and utilizations is clear. These plants are one of the richest plant sources of the country that can be exported too. Iran is considered as one of the best part of the world because of climate, geographical position and growth condition of these plants and in the past has been one of the best source for production and consumption of medicinal plants. As secondary metabolism they produce substances with physiological and therapeutic effects. In this study medicinal plants namely dill ( Anethum graveolens ), savory ( Satureja hortensis ) and pot marigold ( Calendula officinalis ) were evaluated for their host status to root knot nematode, Meloidogyne javanica and effect of this nematode on some pharmaceutical compound of susceptible plants. During the years 2007-2010, infected roots of cucumber, tomato and pomegranate to root knot nematode, were collected from Isfahan and Chahar Mahal va Baktyari provinces. For the identification and mass culture of the collected nematodes from each root sample carrying gall within petri dish in the strill water, a big egg mass was selected and slowly separated from root and placed into a tube containing strill water. Then the selected eggmass was placed around the roots of the 2-4 leaf stage tomato cultivar Rutgers, in the greenhouse. In order to identify the nematode species, after 60-70 days, roots of plants was examined. To confirm ematode species, morphological methods and molecular markers were used and M. javanica was identified according to perineal pattern of adult females and amplification of 670 bp and 1600 bp bands of extracted DNA from egg, single larvae and soil of nematode infected pots. Host status of three plants of dill, savory and pot marigold, was determined using complete randomized blocks design with four replications and after 20 days, three eggs and larvae of nematode per gram of soil was inoculated around the plants roots. After 60 days plant , s root was excised from pot and nematode indice such as gall number, egg number, egg mass number and number of larvae in soil and also according to reproduction factor (RF), dill plant was identified as hypersensitive, savory plant as resistant and pot marigold as susceptible to the nematode. In order to study the effects of different levels of initial nematode population an experiment was designed in complete randomized blocks. After 90 days, using SAS software, means compared by multiple variable Duncan test. According to obtained results, by increasing initial nematode inoculum, ical