Monoclinic hydromagnesite (Mg5(CO3) 4·(OH)2·4H2O) flower-like structures of 2-3 μm diameter have been synthesized at room temperature by a simple precipitation method without using any template, catalyst, or surfactant. The as-synthesized flowers were further calcined at various temperatures to prepare monodispersed, nanofibrous MgO microtubes of aspect ratio ∼15. Both the precursor flowers and the MgO microtubes formed were characterized by powder XRD, TG-DTA, FT-IR, SEM, EDAX, HR-TEM, SAED, BET analysis and photoluminescence (PL) studies. A plausible mechanism for the formation of cubic MgO microtubes from monoclinic hydromagnesite flowers is proposed. The as-synthesized nanofibrous MgO microtubes have shown intense green and red emission. The more defective MgO microtubes formed in N2 atmosphere at 400°C showed the highest PL intensity and surface area. An attempt has been made to correlate the lattice parameter and the PL intensity. © 2007 American Chemical Society.