Abstract: Utilization of the ash generated from coal-fired power plants to reduce heavy metal content in municipal sludge was investigated.By using the coal ash to passivate heavy metals in the sludge to be added to yellow garden soil for a pot experiment, the effect on the growth of Ruellia Brittoniana was monitored. The results showed that the coal ash significantly reduced the heavy metals, especially available Fe and Mn, in the sludge. The passivation effect was most significant when the ratio of municipal sludge to coal ash was 1 to 2 in an 8-hour treatment. By comparison, the phosphor-gypsum addition showed no significant passivating effect on the sludge. The coal ash passivated sludge significantly increased the contents of nitrogen, phosphorus, potassium, and microelements in the gardensoil. Meanwhile the plants grown on the composite soil significantly increased on total nitrogen. Among all mixing ratios, the mixture of equal parts of soil and the passivated sludge allowed the greatest amount of dry matters accumulated in both the above-and underground parts of R.brittoniana, and consequently, was deemed appropriate for urban gardening applications.