This paper focuses on the preparation and characterization of Poly(methyl methacrylate)/multi-walled carbon nanotube composites through ex-situ and in-situ processes. The extent of dispersion and fracture morphology was studied by TEM, AFM, SEM and FESEM. The increase in conductivity at percolated loading of 2.91 wt% was more for in-situ prepared PMMA/MWNTs nanocomposite as compared to ex-situ prepared nanocomposites. The dielectric constant of pure PMMA was increased from 5 to 72 in the ex-situ prepared PMMA/MWNTs nanocomposites with 4.76 wt% of MWNTs loading. Moreover, for the ex-situ nanocomposites containing 2.91 wt% of MWNTs, the dielectric constant was 15, but in-situ prepared PMMA/MWNTs nanocomposite showed two times increase at same loading of 2.91 wt% of MWNTs. Dielectric constant of PMMA/MWNTs nanocomposites loaded with (< 4.76 wt%) of MWNTs remained almost constant with frequency. Dynamic mechanical analysis showed remarkable increase in storage modulus, especially at higher temperatures with 4.76 wt% loading of carbon nanotubes as compared to pure PMMA. The presence of additional peak before T(g) indicated that CNTs could be used to wake up secondary relaxations, which were inactive in pure PMMA. Thermogravimetric analysis (TGA) showed that thermal stability of PMMA/MWNTs nanocomposites increased by 45 degrees C (in N2) and 27 degrees C (in air) at 4.76 wt% of MWNTs as compared to the pure PMMA.