Apart from Hg mining, coal and its by-products were also recognised as one of the major sources of Hg contamination for the environment causing severe health hazard for human and wildlife. Present study investigates phytoremediation potential (PRP) of Hg from flyash (FA) using Brassica juncea. The plants were grown under five different combinations: garden soil (GS) (0% FA + 100% GS), FA25 (25% FA + 75% GS), FA50 (50% FA + 50% GS), FA75 (75% FA + 25% GS) and FA100 (100% FA + 0% GS), and their biometric growth and Hg accumulation in different tissues were observed every month upto 90 days of exposure duration. With increase in time duration, Hg accumulation also increased and mainly accumulated in root followed by stem > leaf however, for FA50 it was root > leaf > stem. Among FA treated combinations, the relative elongation ratio of root and shoot, and their dry biomass increased with increase in time and were significantly higher for FA25 and FA50 combinations. With increase in percentage of FA and exposure duration, the Hg accumulation also increased (R > 0.964) and thus Hg content in substrate decreased (R > 0.852). The bioconcentration factor of root was enhanced with exposure duration however no changes were observed for TF suggesting maximum phytostabilization potential (0.58 mg Hg kg plant). Non-detrimental effect of Hg and higher PRP of 2.62 mg Hg kg plant suggests Indian mustard as a promising accumulator species for phytoremediation of FA-contaminated sites when grown on equal proportion of FA and GS, and can show higher PRP if exposed for longer duration.