Abstarct: Appropriate nutriment and applying novel techniques are known as fundamental methods in elevating rice production. Silica (Si) is a useful element in rice which improves its quality and yield. On the other hand, following nitrogen, potassium has the most effective role in both qualitative and quantitative rice production. Furthermore, weeds serve as a destructive factor influencing rice quality and yield. In order to investigate the effect of applying different concentrations of potassium silicate on rice (Oriza sativa Shirudi variety) in competition with weeds, an experiment was conducted at Iran's Rice Research Institution in 2010. The experiment was organized as factorial baxsed on completely randomized blocks design in 3 replications. Treatments consisted of application of potassium silicate foliar application in different concentrations (5 levels) and growth stages (0, 2.5 g/l at tillering and earring stages and 5 g/l at tillering and earring stages) as the first factor, weeds in tow levels (controlled and uncontrolled) as the second factor. Sampling was performed 10 days following spraying at the earring stage and continued weekly. Results indicated that foliar application of 5 g/l potassium silicate at the earring stage had the most effect on stem dry weight, ear length, total seed number, upper internode diameter, plant height and leaf silica content at the earring stage. Concentration of 2.5 g/l at the earring stage and weed control condition produced the highest leaf area index and 1000 seed weight. Moreover, potassium silicate foliar application and doubling its concentration increased ear number in m2 and number of seeds in ears considerably. The highest yield (952.89 g/m2) was recorded when 5 g/l Si applied in no weed control condition. Spraying 2.5 g/l Si at the tillering stage improved stem potassium content up to 5.81 percentages. When there was no competition with weeds, the highest stem Si content was obtained from 5 g/l Si application at the earring stage. On the other hand, weeds dry-weight which were sprayed at the tillering stage were significantly higher than their weight in the spraying treatment at the earring stage. Different levels of Si foliar application and weed control did not affect the leaf chlorophyll and some qualitative traits such as amylose percentage, gel condensing and gelatinization temperature. By and large, 5 g/l Si foliar application at the earring stage and weed control condition produced better results on the investigated traits.