Instead of directly burning a lignite having low calorific value and peat, the Elbistan lignite (L) and the Adiyaman peat (P) were mixed and leached in an autoclave to obtain an oil to not only provide the demand for energy but also protect the environment. The effects of the peat ratio in the mixture on the properties of co-liquefaction products (oil, char, asphaltene, and preasphaltene) and oil yield were investigated in details. The products were characterized by XRD, FTIR, and elemental analysis. In addition, the composition of the oil was identified by GC/MS, showing that the peat ratio did not affect the chemical composition of the oil due to the high lignin content and the nearly same elemental compositions. On the other hand, the oil yield for a co-liquefaction process was found as 34.3% to be higher than the average value of oil yields obtained from the individual feeds (24.3% for lignite and 28% for peat), showing the synergistic effects between the lignite and peat. The obtained oil was paraffinic-low waxy oil with 5138.62 kcal/kg of calorific value and 0.94 g/cm3 density. Finally, it was suggested that the production of a more valuable product using the peat and the lignite having low calorific value will not only contribute more to the country's economy in future but also be better for the environment, instead of directly burning them.