Multi-wall carbon nanotubes (MWNTs) were mixed with polystyrene (PS) by 20 wt%, which is slightly above the percolation threshold. Temperature (T) dependencies of Seebeck coefficient (5) and resistance (R) for the sample (MWNT-PS) were measured under hydrostatic pressure upto 1.2 GPa. The resistance at ambient pressure showed power law T-dependence (R α T -α) and agreed well with Luttinger liquid (LL) model. The exponent α agrees well with the theory prediction and the experimental data of 'bulk-contacted' single-wall carbon nanotube (SWNT). The α increases slightly under high pressure, suggesting enhanced influence of Coulomb interactions. This could be due to either an increased Coulomb screening length or a reduced Fermi velocity under high pressure. The pressure also increases S slightly. The small magnitude and linearity of S versus T shows that the metallic behavior is kept below 1.2 GPa. The theoretical prediction of pressure-induced metal-insulator transition for SWNTs was not observed. Experiments on SWNT mixed in polycarbonate (PC) is under way.