This study investigates the catalytic pyrolysis of waste lubricating oil using a copper-modified fluid catalytic cracking catalyst (Cu/FCC) for the production of diesel-range hydrocarbon fuel. The influence of catalyst loading (1-3% w/v) and reaction time (60-180 min) on liquid fuel yield was evaluated through response surface methodology (RSM) based on central composite design (CCD). The liquid yield ranged from 79.22 to 90.00%, The corrected quadratic model was statistically significant (R2 = 0.9712) and predicted an optimum liquid yield of approximately 89.37% at a catalyst loading of 2.92% (w/v) and a reaction time of 79.81 min. GC-MS analysis indicated that the condensable product was dominated by higher-molecular-weight hydrocarbons, particularly compounds within the C16-C21 range, while process simulation using Aspen HYSYS supported the predominance of condensable hydrocarbon fractions under the modeled operating conditions. Catalyst characterization confirmed successful Cu incorporation, with the Cu content increasing from 0.0074 wt% in FCC to 0.689 wt% in Cu/FCC. NH3-TPD showed that the total acidity decreased from 2.899 mmol NH3 g-1 for FCC to 1.343 mmol NH3 g-1after Cu modification. BET and XRD analyses indicated that Cu impregnation moderately altered the catalyst texture while largely preserving the FCC crystalline framework. Cu-modified FCC shows potential for the catalytic conversion of WLO into liquid hydrocarbons enriched in diesel-range components.