This study presents a new, facile and fast strategy to synthesize platinum nanoparticles (Pt NPs) in methanol under ultrasonic irradiation. Here, for the first time, methanol was used to reduce Pt2+ to Pt0 in the absence of a reductive and surfactant. The hydroxyl free radical (OH•) liberated from methanol under the sonication effect facilitates the formation of PtNPs by aiding the production of nucleation sites and donating electrons to Pt2+. The results show that the PtNPs with an average diameter of 3.9 nm, high percentage PtNPs yield and pure Pt with face-centered cubic (fcc) structure can be synthesized sonochemically in one minute in the presence of methanol. The catalytic efficiency of the obtained PtNPs for degradation of methyl blue (MB) in an aqueous solution showed a rapid rate of decolorization of MB dye.