The effect of pretreatment on the structure and the related fouling/slagging behaviour of fly ash from brown coal has been investigated. Condensable sodium salts and low melting sodium silicates are known as fouling and slagging materials. Experimental proof is given that less of such components were formed after treatment of Loy Yang brown coal with water and, particularly, with Al compounds. For the range of temperatures applied (1000-1400 degrees C) in a drop tube furnace, the quantity of condensable salts generated was found to depend only on the amount of sodium in Loy Yang coal. Aluminium had the effect of reducing the sodium level by ion exchange and thus the formation of fouling ash components. The stickiness of sodium silicates from this coal was also shown to be reduced by aluminium.