Interfacial adhesion of sisal/coir hybrid fibre reinforced natural rubber (NR) composites has been characterized by restricted equilibrium swelling technique with special reference to the effects of fibre loading, orientation and bonding agent. The swelling parameters of NR composites with and without bonding agent were evaluated with three aromatic solvents, namely: benzene, toluene and xylene, by a sorption gravimetric method. As fibre content and penetrant size increase. the solvent uptake has been found to decrease due to the increased hindrance and good fibre-rubber interaction. The bonding agent added mixes showed enhanced restriction to swelling and it is seen that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V-0 - V-r/V-0) is lower for bonding agent added composites. when compared to an unbonded one. The anisotropic swelling studies were carried out to analyse the extent of fibre alignment and fibre-matrix interaction. In strongly bonded composites. the swelling has been mainly observed to take place in the thickness direction. as attested by Optical photographs. The rubber-fibre interaction has also been examined by Lorenz-Parks and Kraus equations.