The conventional fluids used for heat transfer cannot provide the desired thermal performance due to their poor heat transfer characteristics. Disadvantages of the base fluids can be overcome by forming a suspension of nanoparticles with the base fluid. In this work, the effects of using dolomite/deionized water nanofluid on the thermal performance of thermosyphon heat pipe were experimentally investigated. Nanoparticle concentration and surfactant type (sodium dodecyl benzene sulfonate (SDBS), Triton X-100) were studied as parameters. Three different cooling water mass flow rates (5, 7.5, and 10 g/s) were used in experiments with different heating powers (200, 300, and 400 W) to test heat pipe performance. The results indicated that nanoparticle concentration is an effective parameter in the performance of nanofluids, and SDBS exhibit more favorable characteristics than Triton X-100 as a surfactant. The 36.84% decrease in thermal resistance was observed compared to deionized water and enhancement of 38.75% was achieved in heat pipe efficiency using of dolomite nanofluid containing 2% of dolomite nanoparticle and 0.5% of SDBS under a heating power of 200 W and cooling water mass flow rate of 5 g/s.