A strategy to achieve balanced properties using functionalized carbon nanotubes has been investigated, and its nanocomposite exhibited good performance in mechanical and electrical properties. Polybutyl acrylate (PBA) has been utilized to functionalize multiwalled carbon nanotubes (MWNTs) by in situ atom transfer radical polymerization, resulting in a shell of molecular weight controlled on MWNTs (MWNT-PBA). Poly(L-lactide) (PLLA), which has been pitched on acting as the matrix of the polymers that are compatible with PBA such as poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). A series of PLLA/MWNT-PBA nanocomposites were prepared by solution blending. Morphology, mechanical properties, and electrical properties have been tested, and the results showed that the volume electrical resistance of PLLA/MWNT-PBA nanocomposites decreased by 10 orders of magnitude as the content of MWNTs arrived at its percolation threshold, which is just 1.51 wt %, while the elastic modulus had increased 94.7%, compared to neat PLLA when the content of MWNTs is 2.98 wt %. Optical microscope images exhibited the spherulite morphologies of the nanocomposites while differential scanning calorimetry (DSC) measures showed that the temperature of cold crystallization increased when the content of MWNT-PBA increased.