This study investigates how TiO2/deionized water nanofluids affect the thermal performance of a two-phase closed thermosiphon (TPCT) at various states of operation, according to the surfactant types. A straight copper tube with an inner diameter of 13mm, outer diameter of 15mm, and length of 1m was used as the TPCT, i.e., heat pipe. The nanofluid utilizing in experiments was prepared by mixing the TiO2 nano-particles at the rate of 1.3% and a surfactant at the rate of 0.5% with deionized water. The surfactants used for lowering the surface tension give rise to prevent the flocculation in nanofluids. In order to see the influences of the surfactants on the nanofluid properties, two types surfactants, Triton X-100 and sodium dodecyl benzene sulfonate (SDBS), were selected as nonionic and ionic surfactants and used in this study. The nanofluid was charged with in the ratio of 33.3% (equals to 44.2ml) of the volume of the TPCT. To be able to make experimental comparisons, three different working fluids prepared under the same conditions in the same heat pipe were tested at three different heating powers (200, 300, and 400W) and three different coolant water flow rates (5, 7.5, and 10g/s). The experiments were conducted for both TiO2 and Triton X 100-deionized water nanofluid and TiO2 and SDBS-deionized water nanofluid. The findings obtained from the tests were also compared to each other for showing off to what extent a surfactant affects the nanofluid properties. The maximum improvement in the thermal resistance was achieved by 43.26% in the experiment realized at 200W input power and 7.5g/s cooling water mass flow rate, in which the working fluid is TiO2 and SDBS-deionized water nanofluid.