PdO·1.4H2O 1 prepared in our laboratories, as well as commercially available palladium oxides 2–4 have been found to act as efficient catalysts for the Suzuki–Miyaura reaction in ethanol/water mixture at room temperature in air. Thus, in the presence of 1 mol% catalyst, the reaction between different aryl bromides and arylboronic acids afforded a wide range of functionalized biphenyls in quantitative yield. Catalyst 1 has shown to be the most active for all couples of substrates, and it can be recovered and recycled several times without marked loss of activity. It has been demonstrated by means of suitable tests that the true catalyst is a soluble form of palladium originated by metal leaching from the metal oxide precursor. It is worth of note that the amount of catalyst both in the solution and in the isolated organic product is about 1 ppm.