Evidence indicates that silicon (Si) alleviates diverse stresses by improving the antioxidant capacity and phenolics metabolism of plants. We assessed the effect of sodium silicate (Na₂SiO₃) and calcium silicate (CaSiO₃) on Si and aluminium (Al) uptake, antioxidant performance and phenolics (with antioxidant or structural function) of ryegrass cultivated on an acid Andisol under greenhouse conditions. Ryegrass was treated with either sodium silicate or calcium silicate at gradually increasing doses (250, 500 and 1000 mg Si kg^–1 soil). Yield and concentrations of Si and Al were measured in roots and two shoot cuts. At the first cut, phenols, antioxidant enzymes, antioxidant capacity, lipid peroxidation and lignin production and composition were also determined. Ryegrass supplied with sodium silicate exhibited the highest Si content. Root Si was closely correlated with Al or Si : Al ratio. Shoot Si uptake increased total phenols and activities of antioxidant enzymes (CAT, APX and POD), but reduced lipid peroxidation. Silicon also changed the lignin production and composition in shoots at the highest sodium silicate dose. Silicon uptake reduced the deleterious effect of soil acidity in ryegrass. Sodium silicate had the greatest influence on the antioxidant system through enhancement of phenols production and antioxidant enzyme activation. Peroxidase activity appears to be associated with increased lignin biosynthesis in plants supplied with sodium silicate.