  RX J2309.8+2135 = 1RXS J230949.6+213523 is an X-ray source discovered through
the ROSAT all-sky survey. The object was later identified with a star showing a
spectrum resembling a cataclysmic variable (CV). Schwope et al. (2002,
astro-ph/0210059) recently proposed the spectral type of M3, which would
indicate a small distance. We have detected a large proper motion (~69 mas/yr)
of this object. This detection authenticates RX J2309.8+2135 as a nearby dwarf
nova candidate. Even at a reasonable distance of ~100 pc, which is inferred
from the measured proper motion, the outburst maxima of RX J2309.8+2135 would
reach V~9. RX J2309.8+2135 may belong to a hitherto unidentified class of
long-period CVs with the lowest mass-transfer rates.
