In this study, the liquefaction of Elbistan lignite and the co-liquefaction of Elbistan lignite with the biomass were examined. The biomass type used in this study consists of waste plastic, waste paper, waste mud, and molasses. The dissolution reactions were carried out in tetralin at 350-425 degrees C under nitrogen atmosphere. Mo(CO)(6), Cr(CO)(6), Fe2O3, and MoO3 were used as the added catalysts. The particle size ranged from 0.25 mm to 1.5 mm, the isothermal extraction periods ranged from 30 to 150 min, and the solvent/lignite ratio ranged from 1/1 to 9/1. The results indicated that total conversion and oil C gas conversion obtained during the liquefaction largely changed according to catalyst type, biomass type, and reaction temperature. It is understood that other process parameters, such as particle size and solvent/solid ratio, did not have any important effects. According to the obtained results, optimum process parameters were determined as particle size of 1.5 mm, solvent/solid ratio of 3/1, reaction time of 90 min, and reaction temperature of 400 degrees C. Fe2O3 was selected as the most suitable catalyst type and waste paper as biomass type. In order to reduce liquefaction cost in liquefaction operations, results of the experimental studies showed that using coal + biomass instead of coal, nitrogen instead of hydrogen, and recycled solvent instead of fresh solvent would be more suitable.