A definition of a shielding effectiveness (SE) matrix for small shield cans used to suppress intra-system noise coupling in mobile devices is proposed. Assuming shield cans enclosing a noise source can be modeled as equivalent dipole moments along with integrated circuits (ICs), a new SE matrix for radio-frequency interference analysis is defined as a ratio of equivalent dipole moments with and without a shield can. The equivalent dipole moments are experimentally extracted using a GTEM cell and two types of probes (monopole and loop), which mimic well the radiations of ICs. Furthermore, the estimation of suppression of noise coupling to an antenna using the proposed SE matrix is successfully validated through numerical simulations.