Uniaxial tensile tests were carried on graphene (reduced graphene oxide, RGO)–Al laminated composites with Al lamella thicknesses varying from 1 $μ$m down to 200 nm. It was found that there was a transition in plastic deformation mechanism, from a Hall–Petch-typed mechanism at 500 nm and 1 $μ$m Al lamella thicknesses, to confined layer slip (CLS) of dislocations at the 200 nm Al lamella thickness. Moreover, the strengthening effect of RGO was only demonstrated in composite having 200-nm-thick Al lamellas, which can be rationalized by the enhanced barrier for dislocation de-pinning processes in the CLS mechanism.