This study aims to obtain the best operating conditions including pyrolysis time and amount of catalyst in oil fuel production from reject plastic as raw material with coal fly ash as catalyst based on its yield and characteristics. Both reject plastic and coal fly ash are waste originating from a paper industry in Medan. This research was carried out in three steps: preparation of reject plastic and coal fly ash, oil fuel production and characterization (composition of coal fly ash and density, viscosity and heating value of oil fuel). The main components in the coal fly ash are SiO2, C and Al2O3 that are 30.36%, 27.11% and 24.04% respectively. The yields of oil fuel are in the range of 14.18% - 26.58%. From 12 samples, 10 samples meet the standard density whereas 8 samples meet the standard viscosity for diesel fuel based on ASTM D-975. The best operating condition is achieved when using 15% catalyst with 2 h pyrolysis time that produce oil fuel with the highest heating value.