An orbital angular momentum (OAM)-induced spin splitting is theoretically predicted when a higher-order Laguerre-Gaussian beam is transmitted through a metamaterial slab. The upper bound of this spin splitting is found to be |ℓ|w0/(|ℓ|+1)1/2, where ℓ and w0 are the incident OAM and beam waist, respectively. By optimizing the structure parameter of the metamaterial, as well as the incident angle, the OAM-induced spin splitting can reach more than 0.99 of the upper bound in the cases of both the horizontal and vertical incident polarization states, and the transmitted light fields turn out to be full Poincaré beams. These findings provide a deeper insight into the spin-orbit interaction, and, thereby, facilitate the development of spin-based applications.