  We studied the structure of two old open clusters, NGC 1245 and NGC 2506,
from a wide and deep VI photometry data acquired using the CFH12K CCD camera at
CFHT. We devised a new method for assigning cluster membership probability to
individual stars using both spatial positions and positions in the
colour-magnitude diagram. From analyses of the luminosity functions at several
cluster-centric radii and the radial surface density profiles derived from
stars with different luminosity ranges, we found that the two clusters are
dynamically relaxed to drive significant mass segregation and evaporation of
some fraction of low-mass stars. There seems to be a signature of tidal tail in
NGC 1245 but the signal is too low to be confirmed.
