In this research, we develop oxidation-free low-temperature selective laser sintering process of Cu nanoparticles. We analyze the laser sintered Cu NPs and thermal annealed Cu NPs by SEM and XRD. This process is better than traditional Cu NPs thermal annealing process to prevent oxidation. This process also can be applied to flexible substrates. We fabricate flexible transparent Cu electrode by selective sintering of Cu NPs in grid pattern on PEN.