  Magnetoresistance (MR) of the Bi$_{2-x}$Pb$_x$Sr$_2$Co$_2$O$_y$ ($x$=0, 0.3,
0.4) single crystals is investigated systematically. A nonmonotonic variation
of the isothermal in-plane and out-of-plane MR with the field is observed. The
out-of-plane MR is positive in high temperatures and increases with decreasing
$T$, and exhibits a pronounced hump, and changes the sign from positive to
negative at a centain temperature. These results strongly suggest that the
observed MR consists of two contributions: one \emph{negative} and one
\emph{positive} component. The isothermal MR in high magnetic fields follows a
$H^2$ law. While the negative contribution comes from spin scattering of
carriers by localized-magnetic-moments based on the Khosla-Fischer model.
