Nanoparticles are continuously synthesized from submerged magnesium, zinc, and silver rods 1–2mm in diameter by microwave plasma in pure water at 20kPa. Magnesium-hydroxide nanoplates shaped as triangles, truncated triangles or hexagons with 25–125nm in size are synthesized with a production rate of 60gh −1 . Zinc-oxide nanoparticles formed as sharp sticks with diameters of 50nm and lengths of 150–200nm are synthesized with a production rate of 14gh −1 . Silver nanoparticles with a diameter of approximately 6nm are synthesized with a production rate of 0.8gh −1 . The excitation temperature is estimated by applying the Boltzmann plot method in assumption of local thermodynamic equilibrium. The excitation temperatures obtained from hydrogen, magnesium, and zinc lines are 3300±100K, 4000±500K, and 3200±500K, respectively.