<p>Heat stress is a major abiotic factor limiting maize growth and productivity by reducing biomass accumulation, and inducing oxidative stress. This study investigated the effects of biochar and methyl jasmonate nanoparticles (MJNPs) on mitigating heat stress in maize. The results demonstrated that heat stress significantly reduced shoot and root biomass, leaf area, and the number of leaves due to impaired physiological functions and increased oxidative damage. However, the application of biochar and MJNPs, particularly in combination (HEMN: heat stress + biochar + MJNPs), significantly alleviated these adverse effects. The HEMN treatment resulted in the highest biomass accumulation, enhanced antioxidant enzyme activity (SOD, CAT, APX, POD), and increased levels of osmoprotectants such as proline and glycine betaine. Additionally, biochar improved soil structure and water retention, while MJNPs enhanced stress signaling and antioxidant responses. Together, these amendments effectively reduced oxidative stress markers, including malondialdehyde (MDA), electrolyte leakage (EL), and hydrogen peroxide (H₂O₂), demonstrating their protective role in maintaining cellular integrity and metabolic stability. Furthermore, the application of biochar and MJNPs counteracted heat-induced reductions in carbohydrate, protein, and fat contents while promoting dietary fiber accumulation as a potential protective mechanism. These findings highlight the synergistic effect of biochar and MJNPs in enhancing maize resilience to heat stress. The study suggests that integrating biochar and MJNPs in maize cultivation could be a promising strategy to improve crop tolerance to abiotic stress and sustain agricultural productivity under changing climatic conditions. Future research should explore the long-term impacts and broader applications of these amendments in stress adaptation and crop yield improvement.</p>