We present observations of a young (similar to 3-10 Myr old) brown dwa
rf within the rho Ophiuchi star-forming region. A low-resolution optic
al spectrum exhibits a spectral type of M8.5 +/- 0.5 and strong H alph
a emission (W lambda similar to 60 Angstrom). After demonstrating the
youth of this source through several additional lines of evidence, we
place it on the H-R diagram and use the latest evolutionary tracks to
derive a substellar mass of 0.01-0.06 M.. A more accurate mass estimat
e will require tests of the evolutionary tracks and temperature scales
at such young ages and late types.