The effect of purity of amorphous boron raw materials on properties of the hot pressed SiC doped MgB2 superconductor was investigated. MgB2 superconductors with magnetic Jc over 106 A/cm2 and remaining Jc of 105 A/cm2 at 4.2 K and 5 T were fabricated by hot pressing using both high purity (99.00%) and low purity (88.84%) boron powders. XRD analysis shows that purity of the boron powders has little effect on phase component of the MgB2 samples. If the main impurity in amorphous boron is Mg, low purity low cost boron powder is suitable as one of the raw materials for fabricating MgB2. Particle sizes of boron has significant effect on microstructure and properties of MgB2. Smaller boron particle size leads to smaller grain size of MgB2, higher density, higher lattice distortion, and thus higher magnetic Jc.