A LaB6 single crystal produced at the National Institute for Research in Inorganic Materials was used as an electron source of high brightness with a commercial‐type electron probe microanalyzer (EPMA). A single‐crystal tip of 0.2 mm ϕ×4 mm was cut out from a mother crystal of LaB6 obtained by discharge machining. The tip, held with Ta ribbons by electron beam welding, was mounted in a conventional tungsten hairpin filament holder which is commonly used in electron microscopes (CEM), scanning electron microscopes (SEM), and EPMA. Using this LaB6 emitter in an electron gun of the commercial type EPMA, JAX‐3, instead of the conventional tungsten hairpin, the gun was operated under the same conditions as the tungsten hairpin: vacuum between low 10−4 and high 10−5 Torr, emission current ∼100 μA at 25 kV. It is concluded from a comparison of the scanning electron micrographs obtained with the LaB6 emitter and the tungsten hairpin that the LaB6 emitter can well be used instead of the conventional tungsten hairpins as an electron source of higher brightness for CEM and SEM even in such a low vacuum as ∼10−5 Torr for practical use.