Abstract. Catalytic decomposition is a promising way for chemical upgrading process of low quality oil such as biomass tars. In this experiment, catalytic decomposition of biomass tars was performed over Indonesian low grade iron ore catalyst. This process is carried out in a fixed bedreactor which is equipped with preheater to convert the tars into vapor form. The reaction was studied at the temperature range of 500 – 700°C. The kinetic study of catalytic decomposition of biomass tars is represented using first order reaction. The results show that value of constant of chemical reaction is in range 0.2514 – 0.9642 cm3.gr-1 .min-1 with value of the frequency factor (A) and the activation energy (E) are 48.98 min-1 and 5724.94 cal.mol-1 , respectively. Keywords: tar, kinetic, catalytic decomposition, iron ore