The depleting of fossil energy reserves is a global issue because increasing energy needs. On the other hand, the utilization of palm kernel shells and plastic waste are not optimal. This research aims to find out the characteristic of increasing temperature from heating a mixture of palm kernel shells and PET waste using a microwave oven. Palm kernel shell and PET were mixed in variation of 100:0, 75:25, 50:50, 25:75, and 0:100 shell charcoal used to increase the rate of absorption of microwaves. The thermal treatment was carried out until it reaches a temperature of 105°C. Temperature and mass were recorded per second automatically. Retrieving data on temperature and mass are obtained from recordings per second using data loggers and hyper terminals. The results showed that the heating rate value decreases from 0.6804 ℃ / sec to 0.3285 ℃ / sec. The mass loss rate value decreased from 0.0146 g / sec to 0.0059 g / sec. The value of energy consumption increased from 88 kJ to 171.2 kJ. The addition of PET will have an impact on the decrease in the value of mass loss rate and heating rate but the energy consumption has increased