Amorphous and crystalline (rhombohedral structure with  growth direction) boron nanobelts were synthesized by the vapor-liquid-solid technique. Their structure and chemical compositions were studied by various electron and atomic force microscopy techniques. Most amorphous and crystalline belts have a width to thickness ratio of 2 and are covered with a layer of amorphous silicon oxide. The crystalline belt cores are defect-free single crystals. Gold catalyst thickness and synthesis temperature are the two prominent parameters determining structure of the synthesized nanobelts. The elastic modulus and hardness were measured using nanoindentation and atomic force microscopy three-point bending techniques. The indentation elastic modulus and hardness were measured to be 92.84.5 GPa and 8.40.6 GPa for amorphous belts, and 72.73.9 GPa and 6.80.6 GPa for crystalline ones, respectively. The three-point bending elastic moduli were found to be 87.83.5 GPa and 72.22.4 GPa for amorphous and crystalline, respectively. The measured mechanical properties are 4-5 times lower than those of the counterpart bulk materials.