  The High Mass X-ray Binary Pulsar SAXJ2103.5+4545 has been observed with
INTEGRAL several times during the last outburst in 2002-2004. We report a
comprehensive study of all INTEGRAL observations, allowing a study of the pulse
period evolution during the recent outburst. We measured a very rapid spin-up
episode, lasting 130days, which decreased the pulse period by 1.8s. The spin-up
rate, pdot=-1.5e-7 s/s, is the largest ever measured for SAXJ2103.5+4545, and
it is among the fastest for an accreting pulsar. The pulse profile shows
evidence for temporal variability, apparently not related to the source flux or
to the orbital phase. The X-ray spectrum is hard and there is significant
emission up to 150keV. A new derivation of the orbital period, based on RXTE
data, is also reported.
