The strength, under uniaxial load, of composite gels containing filler particles has been investigated by calculating the stress concentration in the gel matrix. The particles were assumed to be rigid spheres, and the interaction between the particles was taken into account based on a self-consistent model. The bonding between the particles and matrix was treated for two typical cases, (1) perfectly bonded, (2) smoothly connected. For case 1, the analytical result shows that the stress concentration factors decrease with the increasing of the volume fraction of filler. For case 2, the stress concentration factors are independent of the volume fraction of filler. The structural failure caused by the stress concentration was analyzed.