The paper examines the effect of Enterprise Resource Planning (ERP) system implementation on organizational performance efficiency with respect to operational achievements and managerial decision-making in the Libyan administrative environment. The Eastern Region Branch of the Libyana Mobile Company was selected for this study due to the scale of operation and maturity of the technical base at the enterprise. For the research purposes an explanatory quantitative design was used and a field questionnaire applied to 56 employees and ERP users was performed. Six dimensions of ERP system were investigated: data centralization, process automation, decision support, cost reduction, customer services and human resource management. In order to corroborate employees' perceptions, several operational indicators were analyzed with respect to their changes before and after ERP implementation. Multiple regression analysis revealed that the ERP dimensions used in the model accounted for 64% of the variance in organizational performance (R² = 0.64). Data centralization was the highest predictor (β = 0.47), and process automation (β = 0.41) was the second predictor. Analysis of mediation effect found user satisfaction to be a partial mediator of the effect of ERP implementation on organizational performance. Analysis of objective operational indicators indicated a 66.3% decrease in transaction processing time and a 64.6% decrease in operational errors. Also, productivity increased by 60.7%, and operational cost per transaction decreased by 20.0%. Conclusion drawn is that ERP implementation positively affects the organizational performance when technical possibilities are effectively supported by user involvement, change management, data management and training................... Key words: ...................Enterprise Resource Planning (ERP); Organizational Performance; User Satisfaction; Libyana; Digital Transformation; Libyan Administrative Environment.