Sulphur hexafluoride (SFó) gas insulated switchgear (GIS) is widely used in electrical power supply system and therefore needs regular preventive maintenance. In this research work, a reliable and effective diagnostic technique was used to detect SFó byproducts caused by partial discharge (PD) occuring as a result of more that one defect, named as a hybrid defect. A 0.2-MPa presurrised coaxial chamber prototype similar to that used in GIS was used to simulate the decomposition of SFó when partially discharging at 48 kV. Two hybrid defects, namely a protrusion-floating particle and a void-floating, were used. The corresponding detected byproducts using Fourier transform infrared spectrometer are SO2, HF, SOF2, SO2F2, SO2F10, SiF4, CO, and C2F6 for the former, and C3F8 and C2F6 for the later. It was found that the by-product combination together with the by-product concentration can be correlated to the type of hybrid defect. Results also show that the protrusion-floating particle hybrid can be potentially more harmful than the void-floating hybrid.