The unavailability of high quality precursor is encouraging researchers to seek effective ways to fabricate magnesium diboride (MgB
2) wire. Herein, cost-effective amorphous boron powder produced through a diborane (B 2H 6) gas process is investigated for the possibility of further industrial application. A thin carbon layer to encapsulate the boron particles is simultaneously deposited by pyrolysis of hydrocarbon. We found that the carbon-encapsulated amorphous boron has a high upper critical field due to impurity scattering, and thereby, enhanced high-field critical current density.