  We have obtained new rotation measure for 11 pulsars observed with the
Effelsberg 100-m radio telescope, in the direction of the Perseus arm. Using a
combination of 34 published and the 11 newly measured pulsar rotation measures
we study the magnetic field structure towards the Perseus arm. We find that two
pulsars towards l$\sim$ 149$^{\circ}$ (Region 1) and four pulsars towards
l$\sim113^{\circ}$ (Region 2) lie behind HII regions which seriously affects
the pulsar rotation measures. The rotation measure of PSR J2337+6151 seem to be
affected by its passage through the supernova remnant G114.3+0.3. For Region 1,
we are able to constrain the random component of the magnetic field to
$5.7\mu$G. For the large-scale component of the Galactic magnetic field we
determine a field strength of $1.7\pm1.0\mu$G. This average field is constant
on Galactic scales lying within the Galactic longitude range of $85^{\circ} <$
l $ < 240^{\circ}$ and we find no evidence for large scale field reversal upto
5-6 kpc. We highlight the great importance to include the effects of foreground
emission in any systematic study.
