  I determine the expansion of the supernova remnant of SN1604 (Kepler's
supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006.
The measurements were done in several distinct energy bands, and were made for
the remnant as a whole, and for six individual sectors. The average expansion
parameter indicates that the remnant expands as $r \propto t^{0.5}$, but there
are significant differences in different parts of the remnant: the bright
northwestern part expands as $r \propto t^{0.35}$, whereas the rest of the
remnant's expansion shows an expansion $r \propto t^{0.6}$. The latter is
consistent with an explosion in which the outer part of the ejecta has a
negative power law slope for density ($\rho \propto v^{-n}$) of $n=7$, or with
an exponential density profile($\rho \propto \exp(-v/v_e)$). The expansion
parameter in the southern region, in conjunction with the shock radius,
indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for
a distance of 4 kpc. An higher explosion energy is consistent with the results,
if the distance is larger.
  The filament in the eastern part of the remnant, which is dominated by X-ray
synchrotron radiation seems to mark a region with a fast shock speed $r \propto
t^{0.7}$, corresponding to a shock velocity of v= 4200 km/s, for a distance to
SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron
emission requires shock velocities in excess of ~2000 km/s.
  The X-ray based expansion measurements reported are consistent with results
based on optical and radio measurements, but disagree with previous X-ray
measurements based on ROSAT and Einstein observations.
