  We report the discovery of a high proper motion L subdwarf ($\mu$
=0.617arcsec/yr) in the Sloan Digital Sky Survey spectral database. The optical
spectrum from the star SDSS J125637-022452 has mixed spectral features of both
late-M spectral subtype (strong TiO and CaH at 7000A) and mid-L spectral
subtype (strong wings of KI at 7700A, CrH and FeH), which is interpreted as the
signature of a very low-mass, metal-poor star (ultra-cool subdwarf) of spectral
type sdL. The near infrared (NIR) (J-Ks) colors from 2MASS shows the object to
be significantly bluer compared to normal L dwarfs, which is probably due a
strong collision induced absorption (CIA) due to H2 molecule. This is
consistent with the idea that CIA from H2 is more pronounced at low
metallicities. Proper motion and radial velocity measurements also indicate
that the star is kinematically "hot" and probably associated with the Galactic
halo population.
