In this paper, thermal degradation of medical plastic waste (the blends of medicinal plastic bottles and plastic infusion bag) that mainly composed of polystyrene (PS) and polypropylene (PP) is studied under both inert and oxidative atmospheres using in-situ FTIR, TG-MS and TG-GC/MS coupled analyses. Meanwhile, the gas evolution profiles as well as the function groups of the decomposition residues during medical plastic waste thermal degradation are also discussed. The aliphatic C H, aromatic C C and aromatic C H exhibit the dramatically vary with temperature, indicating the medical plastic waste begins vitrifying at about 100 °C, starts degrading around 300 °C and reaches to the maximum near 400 °C in inert atmosphere, produces mainly styrene, benzene, toluene, and small amounts of C 1 –C 4 aliphatic hydrocarbons as the initial pyrolysis products. The aromatic compounds are mainly ascribed to PS degradation, and alkanes and alkenes are mainly originated from PP creaking. It is also found that the gaseous evolution profiles are well consistent with DTG curves in terms of appearance of peaks and relevant stages in the whole temperature range. Compared with thermal degradation of medical plastic waste in inert atmosphere, the initial degradation temperature for the medical plastic waste is shifted to lower temperature, while the degradation rate is reduced significantly in the oxidative atmosphere that produces oxygenated hydrocarbons such as acetic acid, phenol and benzoic acid due to the O-atom attack. Lastly, the initial creaking mechanism together with the secondary reaction pathways of the primary volatiles produced from medical plastic waste thermal degradation are also proposed.