There are various analyses performed to study the heat transfer performance of nanofluid as working fluid in the heat pipe. The studies include the different viscosity, density, specific heat and thermal conductivity effects. However, to consider in terms of cost of material, high thermal efficiency particle with high concentration, for example, gold and diamond would cost higher even though it shows good thermal performance as compared to other nanoparticles. In this research, an experiment is conducted to investigate the heat transfer characteristics by using low concentrations of diamond water, which is less than 1% in Loop Heat Pipe (LHP). The nanofluid consists of three types of mass concentration which is 0.3%, 0.6% and 0.9%. There are two conditions to study the effect of nanofluid to heat transfer performance on LHP in this experiment. The conditions are different flow rate and different heat load application. The LHP performance is evaluated in terms of total thermal resistance (Rt) of LHP, heat transfer coefficient of evaporator and transient temperature distribution. To justify the experiment, the results were compared with ANSYS simulation, which found in good agreement. The significant gain from this experiment is the ability to prove that low concentration of diamond attains higher heat transfer coefficient than water. At the same time, the bubble flow patterns of diamond water in vapor line are found to be smaller than water which indicate higher heat transfer characteristic for working fluid compared with pure water. Thus, there is a potential for low concentration of diamond water nanofluid to be utilized as working fluid, in terms of cost, than using mass concentration of more than 1%.