Owing to the current demand for textiles with new functionalities and improved properties, there has been a continuous effort to modify Polyethylene terephthalate (PET) materials. In our previous study, we demonstrated that Bacillus amyloliquefaciens spores can be incorporated into PET fibres during extrusion. However, the extent to which they can be incorporated without fundamentally changing the properties of the fibres is unknown. In this work, scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical microscopy (OM), differential scanning calorimetry (DSC), a Favimat tensile tester, and Raman and Fourier transform infrared spectroscopy (FT-IR) were used to study the properties of PET/spore fibres. The tensile strength, Young’s modulus and elongation at break were dependent on the spore concentration. Additionally the degree of crystallinity increased slightly, whereas the melting and crystallisation temperatures remained constant at all spore concentration levels. Nevertheless the properties of the fibres fall within the acceptable range of variation and are found to be as good as normal PET fibres.