Samples of Ellajjun oil shale were pyrolysed under nitrogen environment to the final pyrolysis temperature of 550 degrees C. The particle size of the samples under study was varied from 10 to 40 mm. The effect of particle size on weight loss and oil yield was investigated at a constant heating rate of 2-3 degrees C/min. Increasing particle size from 10 to 40 mm decreased the total sample weight loss from 27 to 21% at the same final pyrolysis temperature. At the same time, gas weight loss decreased from 10 to 6%. Oil yield was found to decrease with increasing particle size in the studied range from 92 to 70%. The shale oil produced was distilled in a simple atmospheric distillation unit to give naphtha, gasoline, diesel and residue. The naphtha fraction was found to decrease with increasing particle size. The diesel fraction decreased by 8%, i.e. from 50 to 42%, when particle size was increased from 10 to 40 mm. The kerosine percentage decreased from 35 to 22% with increasing particle size.