Co-firing has become a general practice in conventional pf power plants in western countries nowadays. Knowledge on ignition behaviours, combustion characteristic and possible synergistic effects when coal is co-fired with carbonaceous wastes is of importance to operators in terms of selecting the right coal substitutes for co-firing to prevent problems such as mill fires, to maintain good flame stability, and to achieve targeted emission levels. In this study, a Spanish coal and a South Africa coal were blended with four types of carbonaceous wastes at three different mass fractions. The change in ignition behaviour after blending together with overall combustion characteristics was studied using thermogravimetric analysis. Results showed lowered ignition temperatures at higher blending fraction levels. The decreases in both peak temperatures and burnout temperatures are significant regardless of the type and the amount of carbonaceous wastes being blended in the fuel mixture. These lowered characteristic temperatures would normally result in improved overall combustion performance in utility boilers. Moreover, significant changes in burning profiles of coal blended with the same carbonaceous wastes in different mass fractions (especially those for Tyre Scraps) suggest notable synergistic effects during co-firing.