A novel water-swellable rubber (WSR) composite, modified by a compatibiliser, was prepared by blending poly(dimethylsiloxane) rubber (PDMS) as a matrix and poly(acrylic acid) (PAA) partially neutralised by sodium hydroxide (NaOH) as a superabsorbent polymer. The addition of hydrophilic PAA into hydrophobic PDMS improved water swelling ability but without good durability, mainly due to the poor interfaces between PAA and PDMS. Meanwhile, the tensile properties of the WSR before and after swelling decreased dramatically. With NaOH added as the neutraliser for PAA or with aminopropyltriethoxysilane added as the compatibiliser for PDMS and PAA, water swelling ability and/or durability increased. However, when the compatibiliser and the neutraliser were added together, the water swelling ability and durability of the WSR composites further increased by virtue of the synergistic effects due to the increased interfacial cohesion between the PDMS and PAA.