Considering the positive effects of silicon on salinity resistance by some agricultural plants, an investigation was conducted with a completely randomized design of three replications. The main objective was to determine the effect of silicon on nutrient content and nitrate accumulation in lettuce. Electrical conductivity was adjusted at 3 mmhos/cm through addition of NaCl. Silicon was added through addition of a silicate compound in the ratio of 0, 0.5, 1.0 and 2.0 mM/lit. Mean analysis showed that calcium and magnesium contents of lettuce were increased in 0.5 mM L-1 treatment while a higher amount of silicon decreased the amount of calcium, magnesium and phosphorus. Increasing of Si up to 2.0 mM L-1 increased the amounts of potassium, total nitrogen and nitrate in the plant, whereas the amount of Na was decreased through this addition of silicon.