This study investigates the unique and complementary effects of manufacturing technologies and lean practices on operational performance of manufacturing firms. Despite the importance of understanding how various resources are interrelated within firms, there have been few studies focusing on this area. Using data collected from 186 manufacturing plants in Thailand, we found that both manufacturing technologies and lean practices have unique effects on a range of operational performance dimensions ,including quality, lead- time, flexibility, and cost. More importantly, however, we also found that both organizational resources have complementary (or synergistic) effects on those operational performance dimensions. Based on the research findings, we offer theoretical and practical insights which support the importance of building strong manufacturing technologies and lean practices that maximize operational performance.