Cold plasma is known as a method to enhance the adsorption of proteins on the surface of biomaterials. In this experimental study, the efficacy of oxygen and nitrogen plasma treatment on the activation of Poly L-lactic acid/reduced graphene oxide composite (PLAG) was investigated. For this purpose, the chemical, physicochemical, and morphological characteristics, ability to adsorb amino acid L-tyrosine, and biological behavior of the oxygen and nitrogen plasma-treated composites (PLAG-O and PLAG-N) were studied. Following the exposure to oxygen and nitrogen plasma, (PLAG-O) composites presented more enhancement in Raman C-C and C-H bonds. The evaluation of L-tyrosine adsorption revealed the higher intensity of FTIR C-N, C-C and N-H and Raman C-H chemical bonds and also lower intensity of L-tyrosine UV absorbance in solution medium for L-tyrosine-adsorbed oxygen plasma-treated (PLAG-Ot) compared to L-tyrosine-adsorbed nitrogen plasma-treated (PLAG-Nt) composites. More apparent L-tyrosine island-shaped zones were appeared all over the surface of PLAG-Ot composites through FE-SEM experiment. Moreover, conducting detailed AFM study revealed a higher difference in surface roughness (Ra) of the PLAG-O and PLAG-Ot (140 nm) compared to the PLAG-N and PLAG-Nt composites (25 nm). From the biological point of view, the oxygen plasma-treated composites presented better HDF cell behavior in terms of viability and attachment, as well. According to the results of this study, the oxygen plasma treatment exhibits a higher potential to activate Poly L-lactic acid–reduced graphene oxide composite surface compared to the surface treatment in nitrogen plasma.