  We investigate the dependence of residual rotation measure (RRM) on
intervening absorption systems at cosmic distances by using a large sample of
539 SDSS quasars in conjunction with the available rotation measure catalog at
around 21cm wavelength. We found an excess extragalactic contribution in
standard deviation of observed RRM of about 8.11+/-4.83 Rad/m^2 in our sample
with intervening MgII absorber as compare to the sample without MgII absorber.
Our results suggest that intervening absorbers could contribute to the
enhancement of RRM at around 21cm wavelength, as was found earlier for RM
measurements at around 6cm wavelength.
