Abstract <p>Biochar enriched with nanoparticles, as functional materials, may improve the performance and growth of different plants by improving the physicochemical properties of the soil under salt stress. Thus, this research was conducted in a greenhouse to examine the effects of solid biochar, and biochar enriched with Fe₃O₄, MgO and MgO + Fe₃O₄ nanoparticles on German chamomile (<i>Matricaria chamomilla</i>) plants under different salinity levels (0, 5 and 10 dS/m, as non-saline, low and high salinities, respectively). Solid and enriched biochars enhanced soil pH, nutrients, and water holding and cation exchange capacities, but reduced electrical conductivity and bulk density of the soil under different salinity levels. Sodium absorption, generation of reactive oxygen species, lipid peroxidation, osmolyte accumulation and antioxidant activity of roots in salt stressed plants were diminished in response to biochar-related treatments. However, the potassium, calcium, magnesium, nitrogen, phosphorus, iron and zinc uptakes, root and shoot growth, flowers per plant and flower mass were considerably increased by solid and enriched biochars, especially under low and high salinities. The benefits of biochar enriched with Fe₃O₄ + MgO nanoparticles in improving soil properties, plant physiological performance and salt tolerance of German chamomile were more remarkable than solid biochar. Therefore, addition of enriched biochars to the soil not only improve soil properties and enhance nutrients availabilities to the plants, but can also enhance root activities and tolerance of plants to environmental challenges such as salt stress.</p>