Well hexagonal plate-shaped single crystal of magnesium diboride (MgB2) with the size of 100 mu m has been grown at ambient pressure by evaporating Mg-flux method which is a new practice to grow MgB2 single crystal. The superconducting transition of as-prepared crystals was measured to be at about 33.7 K by superconducting quantum interference device (dc-SQUID) magnetometer. The X-ray powder diffraction (XRD) confirmed the MgB2 phase, and the electron diffraction patterns measured by using high-resolution transmission electron microscope (HRTEM) confirmed the structure of MgB2 single crystal. The single crystal images were observed by scanning electron microscope (SEM) and metallographic microscope (MM). The micromechanism of crystal growth is also proposed through the investigations of SEM and MM. (c) 2006 Elsevier B.V. All rights reserved.