Tall fescue (Festuca arundinacea) typically grows in saline soil or potential saline soil because tall fescue turf often needs to be irrigated. A pot experiment was conducted to investigate the effects of silicon (Si) supplements on the biomass and osmolyte content of two tall fescue varieties (XD and K31) at different soil saline levels. The variety XD is strongly resistant to salinity and K31 is weakly resistant. Above-and underground biomass of both varieties tended to decrease as soil salinity increased. Added Si significantly increased the above-and belowground biomass of XD when soil salinity was 150 mmol/L or below and the belowground biomass of K31 when the salinity was 100 mmol/L or below; it did not affect the aboveground biomass of K31. Silicon supplementation significantly increased the root-to-shoot ratio of XD when the salinity was 150 mmol/L or below and that of K31 at a salinity of 100 mmol/L. Salinity reduced the soluble sugar, soluble protein, proline, and malondialdehyde contents of both varieties. Silicon supplementation did not affect the osmolyte contents of XD. It significantly decreased the soluble sugar content of K31 when it was 200 mmol/L or above and proline content of K31 when the salinity was 100 mmol/L. Silicon supplementation significantly decreased the MDA content of both varieties when the salinity was 150 mmol/L or above, but the magnitude of decrease was greater in XD than in K31. These results indicate that silicon supplementation aids in growth of tall fescue in saline soil, and that this benefit is closely related to the biology of the variety.