<p>The present study investigates the impact of the application of silicon (Si) on seed germination and early seedling growth of chia (<i>Salvia hispanica</i> L.), an important medicinal plant, under salinity constraint. For this reason, chia seed were germinated at 25 ± 1&#xa0;°C for one week under salt stress (200 mM NaCl) with or without the treatment with 1 mM Si. Results indicated that salinity constraint decreased seed germination and impaired significantly (<i>p</i> &lt; 0.001) seedling growth. Conversely, the treatment with exogenous Si neutralized the harmful effects of salt stress by improving the germination percentage (32%), velocity index (34%) and seedling vigor index (138%). In addition, Si alleviated the inimical impacts of salinity and enhanced the ability of the embryo to use seed reserves, in terms of soluble sugars and proteins. Besides, the exposition of chia seed to 200 mM NaCl stress significantly induced oxidative stress, reflected by significant (<i>p</i> &lt; 0.001) accumulations of malonyldialdehyde and hydrogen peroxide, and the percentage of electrolyte leakage. Nevertheless, Si supply alleviated the induced oxidative stress under salinity through a significant raise in the activity of polyphenol oxidase and superoxide dismutase. Additionally, Si treatment considerably (<i>p</i> ≤ 0.01) augmented also the accumulation of proline as an osmoprotectant compound. Furthermore, relative to salt-stressed seed without Si treatment, Si significantly reduced the sodium accumulation in seed tissue. These findings suggest that Si had a biostimulatory effect on seedlings emergence of <i>S. hespanica</i> L. under salinity constraint, by modulating the use of seed reserve by the embryo and inducing an antioxidant defense system.</p>