Microplastic (MP) pollution is an emerging threat to soil health and ecosystem services. The harmful effects of the emerging pollutant MP on soil nematodes and plants have been widely studied; however, there is limited research on how to mitigate the damage caused by MP. Previous studies have shown that selenium (Se) plays a significant role in alleviating various stresses; its role in alleviating microplastic impacts remains unexplored. This study aims to investigate the effects of high-density polyethylene (HDPE) MPs and exogenous Se potential on barley plants and soil nematode communities. MP treatment reduced total chlorophyll content, plant height, shoot fresh weight, and root fresh weight by 57.9 %, 14.8 %, 23.1 %, and 35.7 % respectively, compared with the control. Under MP, Nematode abundance and genus richness also declined by 66.3 % and 46.7 %, respectively. Se supply of 10 mg kg−1 partially restored nematode communities, shoot and root biomass by 33.5 % and 26.2 % under MP stress, and advanced spike emergence by ∼14 days. Se supply suppressed Abscisic acid, hydrogen peroxide, and Malondialdehyde levels, alleviating stress signaling, increasing cis-zeatin and Jasmonic acid by 236.6 % and 171.7 % respectively. In parallel, soil enzymes, including urease, dehydrogenase, and alkaline phosphatase, were significantly improved. Notably, bacterivorous nematodes dominated under low Se, whereas high Se (50 mg kg−1) shifted the community toward herbivores. Overall, low Se significantly alleviated MP-induced damage. Our findings offer novel insights into the stress-alleviating potential of Se in microplastic-polluted soils, thereby improving agroecosystem functioning and soil health.