The efficiency of two-phase closed thermosyphon (TPCT) with nanofluid as working fluid under magnetic field effect was investigated experimentally. In this study, silver/water nanofluid with different concentration (20 to 80ppm) is tested. Also, magnetic field with various strength (0.12, 0.35 and 1.2 T) exerted to TPCT by permanent magnet. It was seen that the TPCT heat transfer performance and the thermophysical properties of the base fluid are considerably affected by the nanoparticles addition and magnetic field. According to the experimental result, the thermal efficiency of thermosyphon significantly increased with the nanoparticles concentration increasing as well as magnetic field strength, and the TPCT shows better performance in the highest value of concentration (80 ppm) and magnetic field (1.2 T). Moreover, the experimental results represent that thermal efficiency in the presence of magnetic field somewhat increases.