The elastic modulus and failure behavior of poly(urea-formaldehyde) shelled microcapsules were determined through single-capsule compression tests. Capsules were tested both dry and immersed in a fluid isotonic with the encapsulant. A shell-theory model for a fluid-filled microcapsule was utilized to extract the modulus of the shell wall material from individual capsule tests. The testing of capsules immersed in a fluid had little influence on mechanical behavior in the elastic regime. The average capsule shell wall modulus was determined to be 3.7 GPa. Capsule diameter was found to have a significant effect on burst strength, with smaller capsules sustaining higher stresses before burst.