The generation of problematic Ni-loaded waste from several applications alongside the high cost of the metal catalysts has caused the research effort to develop low cost Ni-catalysts. Therefore, the aim of this work is the study of the catalytic effect of nickel ions onto the thermal decomposition of the olive tree pruning (OTP) in nitrogen and oxygen-based atmospheres via thermogravimetric analysis. Experiments were carried out for the raw and Ni-OTP at three heating rates (5, 10 and 20 degrees C/min) and in three different reaction atmospheres (N-2, 90% N-2-10% O-2 and 80% N-2-20% O-2). Results showed a slight displacement of the curves rightward in the first half of the curve for the Ni-OTP. Besides, the residual mass fraction was lower for Ni-OTP than for the raw one, changing the values from 24.59 to 15.94 for N-2 atmosphere, from 10.45 to 4.11 for atmosphere with 10% of O-2 and from 4.26 to 3.03 for atmosphere with 20% of O-2. This behavior could be due to the inhibitory and catalyst effect that would be produced by the presence of nickel in the solid during the different stages of the thermal degradation. Besides, the environmental implication of presence of nickel during the thermal processes was analyzed and no negative environmental effect was observed. (C) 2016 Elsevier Ltd. All rights reserved.