In this paper, we report on the low temperature solution reduction method employed in the synthesis of large quantities of nano/micro-sized bismuth (Bi) crystals with sodium hypophosphite (NaH2PO2 center dot H2O) as reductant in acidic solutions. The achieved Hi crystals exhibited plate-like (100 nm in size and few nanometers in thickness) or polyhedral (500 nm in size) shapes. Hi nanocrystals transformed to octahedron-like Bi microcrystals only by prolonging the reaction time. The assembly and oriented growth should be the reason. To understand the growth mechanism, we also discussed the possible growth of the Hi nanocrystals exhibits influence of experimental parameters such as reaction time, NaH2PO2 center dot H2O concentration, and pH value. The resulting Bi crystals were characterized by using scanning electron microscopy, X-ray powder diffraction and differential thermal analysis and thermogravimetry. Optical properties of the samples were studied by ultraviolet-visible spectroscopy. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.