Multiwalled carbon nanotubes (MWCNTs) were functionalized with 4-mercaptobenzoic acid in a polyphosphoric acid/phosphorous pentoxide medium to produce 4-mercaptobenzoyl-functionalized MWCNTs (MB-MWCNTs). Gold nanoparticles (GNPs), stabilized by trisodium citrate, were prepared from the in-situ reduction of gold(III) chloride trihydrate by sodium borohydride in the presence of MB-MWCNTs dispersed in ethanol. The morphology of the resulting GNP/MB-MWCNT hybrid showed that GNPs were formed with an average diameter of 4.3 nm, and these were uniformly deposited on the surface of the MB-MWCNTs. High resolution transmission electron microscopy and X-ray photoelectron spectroscopy studies revealed that the GNPs had a well-defined crystal structure. Cyclic voltammetry results showed a high electrocatalytic activity and electrochemical stability of the GNP/MB-MWCNT hybrid in both acidic and basic media.