Highly boron-doped diamond (BDD) was deposited on chemically etched micrometer-sized tungsten wires using microwave plasma assisted chemical vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diameter (about 5 μm) and 250 μm in length could be made successfully. In addition to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidation of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a constant current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanalysis.