This study examines the contribution of firms' open innovation strategies to R&D efficiency at the firm level. R&D efficiency is measured by using Data Envelopment Analysis. Then Tobit regression identifies the effect of open innovation strategies - R&D outsourcing, external funding and introduction of foreign technologies - on R&D efficiency. Results imly that R&D outsourcing strategy is very effective to improve R&D efficiency and large-sized enterprises and low technology industries have larger effect than the others. On the other hand, external funding fails to improve R&D efficiency even though it contributes to expansion of R&D scale. Last, introduction of foreign technologies has negative effect to R&D efficiency in large-sized enterprises and low technology industries.