The current development of modern electronics toward miniaturization and multifunctionalization leads to accumulation of considerable heat, which results in the thermal failure or even explosion of modern electronics. The rapidly increased thermal load requires faster and more effective heat dissipation. Therefore the thermal conductivity of materials has attracted much attention in modern electronics. This work has been carried out to study the effect of addition of boron nitride nanosheets (BNNSs) and nanocellulose (NC) on the thermal and mechanical properties of a polylactic acid (PLA) matrix. Boron nitride (BN) appears to be a potential additive inorganic material for polymers due to its superior thermal conductivity and mechanical properties. Futhermore cellulose nanoparticles, prepared from microcrystalline cellulose by acid hydrolysis, have a small aspect ratio and have received great research attention due to their unique physical and chemical properties and the inherent abundance, renewability and sustainability. In the present study, polylactic acid (PLA) samples containing 0-10 wt% boron nitride (BNNS) and/or nanocellulose (NC) were prepared by solvent casting method. To have an insight into the structure of the composites, phase morphologies were studied using Scanning Electron Microscopy (SEM). Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) analyses and tensile tests were carried out to characterize the thermal and mechanical properties of the prepared composites. Both BNNS and NC improved the thermal conductivity, tensile strength and modulus of the polymer matrix at a low content.