Rod-shaped nanoparticles of alpha-MnSe and MnSe2 were hydrothermally synthesized via the reaction of Mn(CH3COO)(2.)4H(2)O with Se and hydrazine hydrate in NaOH solution at 100-180degreesC for 12h. X-ray diffraction (XRD) analysis indicated that the products were single phase of pyrite manganese diselenide and cubic manganese selenide, respectively. Transmission electron microscopy (TEM) observation shows that the rods have diameter 100 and 200 nm for MnSe2 and alpha-MnSe, respectively. Nanocubics of a-MnSe and MnSe2 with a uniform diameter about 80 nm were also observed in the product. The formation of the nanorods was found kinetically controlled and determined by the concentration of Se2- in the solution. (C) 2003 Elsevier B.V. All rights reserved.