To evaluate the impacts of various concentrations of multiwalled carbon nanotubes (0, 500, 1000 and 2000 mg L^-1) and sodium nitroprusside (0 and 100 μM as nitric oxide (NO) donor) on seed germination and early seedling growth of barley, two separate factorial experiments were conducted based on a randomized complete block design under polyethylene glycol-simulated drought stress and NaCl salinity stress conditions. Based on the results, a concentration-dependent declining trend was observed in barley germination indices upon seed exposure to polyethylene glycol (PEG) and NaCl suspensions. Employing multiwalled carbon nanotubes (MWCNTs) particularly 1000 and 500 mg L^-1 and sodium nitroprusside (SNP) alleviated the adverse impacts of drought and salinity stresses. However, applied MWCNTs and SNP together were more efficient than suspension alone. The combined application of MWCNTs with SNP increased germination percentage, germination rate, root length, shoot length, vigor index and decreased mean germination time of barley. Similarly, the amount of moisture content and uniformity of seed germination were obviously increased by MWCNTs and SNP under drought and salinity. In contrast, MWCNTs at 2000 mg L^-1 had an inhibitory impact on barley seed germination, while use of SNP moderated adverse effects of MWCNTs. Generally, it can be concluded that appropriate concentration of MWCNTs is beneficial in improving drought and NaCl salinity tolerance of barley by boosting seed water absorption and increasing the moisture content of seedlings.