The thermal performance of a closed-loop flat plate pulsating heat pipe filled with water-based binary mixtures and the corresponding pure liquids as working fluid is investigated experimentally at a 60% filling ratio. The experiments are reported for the gravity-assisted mode. The evaporator section is at the bottom, the condenser section at the top, and in between a well-insulated adiabatic section. The evaporator section is heated using cartridge heaters, and the condenser section is maintained at 22°C. The flow regime inside the flat plate pulsating heat pipe is captured using a high-speed camera. The dry-thermal resistance is around 0.5 K/W (for all heat inputs). The thermal resistance (R) decreases with increased heat input (Q_in) and volume percentage of ethanol in the binary mixture. The smallest measured resistance is 0.2 K/W for the case of pure ethanol at Q_in = 160 W. The slug-plug oscillations and the flow frequency from the evaporator to condenser increase with the increase in Q_in and %vol of ethanol. These phenomena are attributed to the relatively larger saturation pressure gradient versus temperature (dp/dT)_sat and lower boiling point and surface tension for ethanol than water.