Mirrored aperture synthesis (MAS) has been proposed to utilize a few antennas to provide high spatial resolution for Earth remote sensing. But the sensitivity of MAS is not completely analyzed. For this problem, the characteristic of the noise in 2-D MAS is derived. Further, both the sensitivity of 1-D and 2-D MAS are analyzed. Numerical simulations are carried out to evaluate the sensitivity of a MAS system, and comparisons between the sensitivity of MAS and traditional aperture synthesis are made.