The poly(l-lactide) (PLLA) biocompatible and biodegradable polymer was reinforced with functionalized Multiwalled carbon nanotubes (MWCNTs) to overcome on insufficient mechanical properties of this polymer for high load bearing applications. To fully realize the potential of MWCNTs for this purpose, they have to be homogeneously dispersed in polymer matrix and have efficient load transfer across the MWCNTs/polymer interface. The pristine MWCNTs (pMWCNTs) were functionalized, at first, by Friedel-Crafts acylation, which introduced the aromatic amine groups on the sidewall of MWCNTs (MWCNT-NH2) without shortening or cutting of pMWCNTs. And then, the PLLA chains covalently grafted from the sidewall of MWCNT-NH2 by in situ ring-opening polymerization of l-lactide oligomers using stannous octanoate as the initiating system. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy spectra revealed that the PLLA chains grafted form the sidewall of MWCNTs strongly. The surface morphology of pristine and PLLA-grafted MWCNTs (MWCNT-g-PLLAs) was characterized by scanning electron microscopy and transmission electron microscopy. The tensile test of prepared composites of PLLA with various concentrations of MWCNT-g-PLLAs show a significant increment in tensile strength and elongation at failure of composites with increasing the concentration of MWCNT-g-PLLAs in composites. Also, it is found that the MWCNT-g-PLLAs increased the photoluminescence effect of PLLA and widened the luminescence region of PLLA.