Experimental work has been undertaken using a radiation method to ignite single coal particles and to study their ignition behaviour. Particle sizes used were in the range of 600 mu m - 1800 mu m. Effect of particle size on ignition temperature and ignition time was investigated for three types of coal under conditions of constant heating rates. Results show that under these conditions, ignition temperature increases with particle size contrary to the widely reported trend of decreasing ignition temperature with increasing particle size. It was also found that ignition temperature increases with heating rate. When particles of different sizes are heated by the same power, smaller particles experience higher heating rates than larger ones. The effect of particle size on ignition time was found to be the same as reported by other researchers where ignition time increases with particle size.