ZnMoO4 with a rhombus sheet or flower-like structure, alpha-ZnMoO4 and needle-like ZnMoO4 center dot 0.8H(2)O were successfully synthesized by simple hydrothermal crystallization processes with citric acid. ZnMoO4 center dot 0.8H(2)O was easily synthesized in a shorter reaction time (2 h) at a higher reactant concentration. It gradually transformed into ZnMoO4 with a monoclinic wolframite tungstate structure with an increased reaction time, and pure ZnMoO4 was obtained with a longer reaction time (8 h). Citric acid (CA) played an important role in controlling the morphology of the as-obtained molybdates. The alpha-ZnMoO4 and ZnMoO4 were synthesized by heating ZnMoO4 center dot 0.8H(2)O at 130 degrees C for 4h and 8 h, respectively, under hydrothermal conditions. With transforming of ZnMoO4 center dot 0.8H(2)O to alpha-ZnMoO4 and further to ZnMoO4, the needle-like crystals gradually disappeared and were transformed into crystals with rhombus sheet morphology and then further to pentacle or flower-like crystals that can be ascribed to continuous splitting and growing of the rhombus sheets. (C) 2010 Elsevier B.V. All rights reserved.