High strength application of biopolymers requires good mechanical strength. The tensile properties of polylactic acid (PLA) are relatively low for major industrial applications such as packaging, biomedical and automobile spare parts. In this study, the mechanical strength of polylactic acid was enhanced with nanocarbon isolated from diesel engine combustion soot. The isolated nanocarbon was characterised using spectrometry and Fourier transform infrared (FTIR) spectroscopy analysis. After that, the nanocarbon was used as a reinforcement in plasticised PLA to produce a composite. The PLA-nanocarbon composite was produced using the compression moulding technique. The nanocarbon composition was varied between 2 wt% and 8 wt% in the PLA matrix. The tensile, hardness and morphological properties of the composite were analysed with the tensile test, hardness test, optical microscope and X-ray diffraction (XRD) analysis. The ultraviolet (UV) spectrometer and FTIR analysis results confirmed the successful isolation of nanocarbon from the diesel engine combustion soot. The tensile and hardness properties of the PLA matrix increased with addition of nanocarbon. The morphological images showed good miscibility between the PLA and the nanocarbon reinforcement, responsible for the increase in mechanical properties. The potential use of the composite for high strength application showed great possibility based on the result obtained.