The hybrid photovoltaic and thermal (PV/T) system can utilize solar energy more effectively and has a higher total efficiency compared with a traditional solar collecting system and a photovoltaic (PV) module. However, there is limited experimental data on how much energy the PV/T system can save when operating with same area of a PV plate and a solar collector simultaneously. In this paper, a comparative test rig had been set up to measure and analyze the performance of PV/T system. There were monocrystalline silicon PV/T solar collector, a traditional solar collector and a monocrystalline silicon photovoltaic plate. The PV/T collector and the traditional solar collector had the same collecting areas and solar cell covered area of the PV/T collector was the same as the area of the photovoltaic plate. The experimental results showed that the daily thermal efficiency of PV/T system was about 40%, which was about 75% of that for a traditional solar thermosiphon system, and the daily average electrical efficiency was found about 10%, which was a little lower than the photovoltaic module. But primary-energy saving efficiency of the PV/T system was much higher than that of the individual PV plate and the traditional solar collector. ► The paper presents an experimental study on PV/T system under natural circulation. ► Test and control groups provide much comparative data between different system. ► We clarify effectiveness of PV/T system by comparing with two control groups. ► The results of experiment are useful in designing and evaluation of PV/T system.