A series of palladium/multi-walled carbon nanotube (Pd/MWCNT) catalysts were prepared for the total oxidation of methane. Their morphologies, thermal stabilities and redox properties were investigated using different analytical techniques. Their textural properties were also measured by the Brunauer-Emmett-Teller method. On this basis, the catalytic behaviors were tailored by pretreating with mixed acid solutions and changing the MWCNT diameters. The results show that higher MWCNT diameters improved the Pd dispersion and enhanced the catalytic properties of the Pd/MWCNT. A proper ratio of HNO3 to H2SO4 can provide moderately active sites such as oxygen-containing groups (OCG) and defects, on which the Pd precursor can be attached or anchored. Excessive H2SO4 will deteriorate the carbon framework and lower the frequency of OCG decorated on the outer surface of the MWCNT. As a result, the activity of the Pd/MWCNT catalysts for methane oxidation is suppressed.