Abstract Widespread occurrence of arsenic (As) in paddy agricultural fields and consequent accumulation of As in rice grains poses a great threat to human health. In the present study, the approach of co-culture of rice (Oryza sativa) and Hydrilla verticillata was studied to evaluate arsenic toxicity amelioration in rice. Rice plants of two varieties, Pooja and CO-50, grown under As stress (25 μ M) for 10 d showed significant decline in growth, photosynthetic pigments and protein content while an increase in malondialdehyde (MDA) and non-protein thiol (NP-SH) contents and guaiacol peroxidase (GPX) activity. The effects were attributable to significant As accumulation in both Pooja (185.35 μ g g−1 dw in root and 23.49 μ g g−1 dw in shoot) and CO-50 (846.61 μ g g−1 dw in root and 167.32 μ g g−1 dw in shoot). In rice-Hydrilla co-culture, significant improvement in growth and various biochemical parameters were observed in both varieties of rice as compared to As alone treatments. A significant decrease in As accumulation was also noticed in both Pooja (93.23 μ g g−1 dw in root and 8.37 μ g g−1 dw in shoot) and CO-50 (566.19 μ g g−1 dw in root and 94.36 μ g g − 1 dw in shoot). Hydrilla plants itself showed significant As accumulation when grown in co-culture with Pooja (476.36 μ g g−1 dw) or CO-50 (439.43 μ g g−1 dw). In conclusion, the co-culture of hydrilla plants with rice can be used as a low-cost, sustainable and feasible technology to ameliorate As toxicity and to reduce As accumulation in rice.