This paper studies the rheological properties of ultrathin aminomethacrylate membranes that are synthesized at the interface between oil and water. We have measured the kinetics of the crosslinking reactions, the zero shear modulus, and the nonlinear rheological properties of those two-dimensional networks. The measurements were performed at a planar interface using a special surface rheometer. Once stabilized, the membranes exhibit rubber-elastic properties. In addition, we have formed small emulsion droplets using the same type of interfacial polymerization. In order to get more information on the mechanical properties of the resulting microcapsules, we have developed a new experimental technique that consists in measuring the deformation of a capsule in a spinning drop apparatus. A theoretical analysis of the deformation process allows an interface apparent elastic Young modulus to be calculated. From a comparison of the surface shear modulus with the Young modulus, it is then possible to estimate the surface Poisson ratio, which is here approximately zero. These results point to the existence of area compressible anisotropic membranes.