In Peru, the generation of plastic waste is growing and becomes a pressing environmental problem, only 0.3% of plastic waste is recycled. This research work seeks to study the variables that affect the pyrolysis of high-density polyethylene (HDPE) waste to obtain the maximum performance of liquid fuels. The effect of particle size and operating temperature on the yields of liquid products was studied. 30 kg of HDPE waste composed of different particle sizes were acquired up to a maximum of 8 mm, the HDPE residues were sieved and classified into four groups, later the sample was characterized and compared against a standard. A laboratory-scale system for pyrolysis was designed and built in which the operating conditions that maximize the obtaining of liquid fuels were an operating temperature of 550 °C, operating pressure of 34.66 kPa abs., heating rate of 20 °C/min and a particle size of 4 to 6 mm. The yields of products obtained were the following: 88% of liquids, 2% of solids (carbonaceous residue) and 10% of gases.