A hydroponic experiment was carried out to examine the effect of H2 S in alleviating chromium (Cr) stress in barley. Two factorial design with six replications was selected including three levels of NaHS (0, 100 and 200 µM) and two levels of Cr (0 and 100 µM) as treatments. The results showed that NaHS addition enhances plant growth and photosynthesis slightly as compared to the control. Moreover, NaHS alleviated the inhibition in plant growth and photosynthesis by Cr stress. Higher levels of NaHS exhibited more pronounced effects in reducing Cr concentrations in roots, shoots and leaves. Ultrastructural examination of plant cells supported the facts by indication of visible alleviation of cell disorders both in root and leaf with exogenous application of NaHS. Increased number of plastoglobuli, disintegration and disappearance of thylakoid membranes and starch granules were visualized inside the chloroplast of Cr stressed plants. Starch accumulation in the chloroplasts was also noticed in the Cr treated cells, with the effect being much less in Cr + NaHS treated plants. Hence, it is concluded thathydrogen sulfide (H2 S) produced from NaHS can improve plant tolerance under Cr stress. Environ Toxicol Chem © 2013 SETAC.