In this paper, amino acid functionalized multi-walled carbon nanotubes (f-MWCNTs)/poly(amide-imide) (PAI) nanocomposites (NCs) were prepared by a solution mixing method. First, 4,4'-methylenebis(3-chloro-2,6-diethyl trimellitimidobenzene) reacted with 3,5-diamino-N-(4-hydroxyphenyl)benzamide in tetra-n-butylammonium bromide as a green medium and a safe methodology (toxic and volatile organic solvents were eliminated) to produce a nanostructured PAI in high yield. MWCNTs were chemically modified with S-valine using microwave irradiation in order to obtain a homogeneous dispersion of MWCNTs in the PAI matrix. The resulting NCs were also characterized by FT-IR, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and thermogravimetric analysis. The TEM and FE-SEM images confirmed good dispersion of f-MWCNTs in the polymer matrix. The results of TGA analysis suggest that a good thermal stability occurs especially with low filler amounts (5 wt%) of f-MWCNT.