Indonesian people's awareness of waste is still very low, especially regarding plastic waste, which until now has not had any significant further processing to reduce the negative impact on the environment. So far, people have only burned plastic waste without any processing to make it into more useful raw materials. There is an increasing accumulation of plastic waste and its handling is still less than optimal because most of it is just thrown away or burned. With the latest technology, it is possible for plastic, especially LDPE, to be processed into alternative fuel. However, this plastic oil does not meet good fuel standards for use directly in engines. The performance of vehicle engines, especially generators, is very dependent on the fuel used, such as Pertamax. Pertamax quality is determined by the cetane number, which affects motor power. the higher the cetane number, the better the performance. However, fuel with a high cetane number tends to have a higher price. With a composition ratio of LDPE and Pertamax plastic waste oil of 50%/50%, 20/80% and 30/70%. This research was carried out experimentally on a YAMAKOYO GFH 4500 LX brand generator engine with fuel mixed with LDPE and Pertamax plastic waste oil. When using Pertamax fuel and plastic waste oil with a ratio of both 50%, it produces the highest torque of 10.43 Nm at a load of 3000 W and the highest power of 2.59 HP at a load of 3000 W. At a ratio of 70% Pertamax to 30% LDPE plastic waste oil. the highest torque is 11.43 Nm at a load of 3000 W and the highest power is 2.8 HP at a load of 3000 W. On a mixture of 80% Pertamax fuel and 20% LDPE plastic waste oil the highest torque is 13.77 Nm at a load of 3000 W and the highest power 2.89 HP at 3000 W load.