Fourier transform infrared spectroscopy (FTIR) is a vibrational spectroscopy used to gain structural information about a sample. The advantage of FTIR for structural analysis is it is a non-contact technique; only a small quantity of sample is needed (∼ 1 mgmL -1 ); the sample can be probed in different physical environments like the solid state, liquid state and when adsorbed to a surface; the sample preparation is minimal and a spectrum can be obtained in a few minutes. For systems with multiple components like polymer-peptide microspheres, FTIR can be used to identify the individual components, and interactions between the components which shift the peaks. Terahertz time-domain spectroscopy (THz-TDS) is a valuable technique which can be used to detect T g,α and T g,β , associated with the α-and β-relaxation processes respectively. It is a relatively recent technique which is used to investigate the molecular dynamics of relaxation processes at high frequencies. The advantage of this technique is that it is a non-contact technique and can measure molecular mobility of a material over a broad temperature range over the spectral region of 0.1 -3 THz. It can be used to investigate the microscopic mechanisms of amorphous polymer dynamics. In the present study we examine samples of freeze-dried microspheres with different concentrations of encapsulated peptide. In addition to the physical characterisation, we investigate the molecular mobility of these materials and the behaviour and trends these exhibit with respect to the temperature dependance using THz-TDS. Thus, the purpose of this work is to provide a comprehensive understanding of the relationship between the relaxation dynamics and the molecular structure of PLGA microspheres with varying exendin-4 peptide concentrations, and to rationalise the behaviour of these materials in relation to T gα and T gβ .