  To test the model of the polarized gluon distribution $\Delta G(x, Q^2)$ in
the proton, we propose a new process, diffractive $\Lambda_c^+$ productions in
polarized $pp$ reactions, which will be observed in the forthcoming RHIC and
also the proposed HERA-$\vec {\rm N}$ experiments. The spin correlation between
the target proton and the $\Lambda_c^+$ produced in the target fragmentation
region largely depends on $\Delta G(x, Q^2)$ and thus, the process is quite
promising for testing the models of $\Delta G(x, Q^2)$.
