roomrape ( Phelipanche . ) is the most important root parasitic weed in farm lands. Broomrape is found mainly in the Mediterranean region, South-East Europe, Middle East, West Asia and North Africa. Due to close physiological relationship with its host and disruption the activities of metabolic of plants, it reduces both production and quality of plants. Various methods are considered for the management of broomrape but none of these methods are effective to control this weed. Fertilizer and soil fertility management can be effective in reducing the damage caused by broomrape. Silicon (Si) is the second most abundant element after oxygen in the soil. Approximately, 31% of the Earth's crust occupied by this element. Although silicon as an essential element in plants has not been considered, reports suggested its beneficial effects on plant growth. Therefore, a study was conducted to investigate the effect of silicon on the tomato growth and its resistance to broomrape. Seeds of susceptible and resistance cultivars of tomato were planted in pots in a bed of sand and perlite. Silicon treatment was applied at three levels including zero, 1and 1.7 milimolar. Results showed that in terms of broomrape infection of tomato, the level 1.7 milimolar of silicon increased the number of days until the first appearance of broomrape. The minimum number of tubercle, height and number of stems of broomrape also obtained from the level 1.7 milimolar of silicon. Lowest level of shoot and root dry weights of broomrape were associated with 1.7 milimolar silicon. Consumption of silicon was not effective in increasing the height of the tomato plants but between susceptible and resistant cultivars of tomato to broomrape, maximum height associated with the level of 1 milimolar silicon. Silicon consumption did not affect the chlorophyll content and dry weight of tomato. Silicon at 1.7 milimolar increased tomato leaf area compared with other levels of silicon. But increases consumption of silicon had not a positive effect on root dry weight of tomato. The use of silicon had no effect on activity of tomato antioxidant enzymes. In this study according to the effect of silicon on the morphological characteristics of broomrape and tomato plants, the positive role of silicon is more noticible on the characteristics of broomrape. One reason maybe that the tomato is silicon absorption rejective. So tomato not able to absorb high levels of silicon and much of silicon remains at the root surface. On the other hand it might be that increasing of silicon caused resistance to broomrape due to the creation of physical barriers in the tomato root and limited penetration of tubercles of broomrape into the host tissue.