Here the effect of tea tree and manuka essential oils (EOs) on the mechanical properties and antibacterial activity of electrospun polylactic acid (PLA) fibres is investigated. It is found that the essential oils work as plasticisers for PLA, lowering the glass transition temperature of the resulting composite fibres up to 60% and increasing elongation-at-break and tensile strength up to 12 times. Manuka EO is particularly successful in blocking the formation of biofilms of Staphylococcus epidermidis that is typically involved in nosocomial infections associated with implanted devices. The results demonstrate that natural extracts can be used to control the mechanical behaviour of PLA fibres and to confer antibacterial activity.