Abstract: The Chinese FengYun-3 (FY-3)A satellite was successfully launched on May 27, 2008, with a Microwave Temperature Sounder (MWTS) onboard. MWTS has four channels with frequencies of 50.3, 53.596, 54.94, and 57.29 GHz, respectively. The MWTS measurements are primarily used for profiling atmospheric temperatures from surface to lower stratosphere. MWTS is a cross-track scanning instrument, and its Earth-view measurements are calibrated through the warm target and cold space measurements during every scan cycle. In this paper, the FY-3A MWTS and its channel characteristics are first introduced. The calibration process and the postlaunch instrument performance are then presented, including the long-term trends of noise equivalent differential temperature (NEDT), calibration counts from cold space and warm targets, instrument telemetry, and channel gains. The observed and simulated brightness temperature (BT) differences of MWTS and Advanced Microwave Sounding Unit-A (AMSU-A) are compared. It is shown that the MWTS NEDT values at all channels are much better than its specification. The BT biases of MWTS channels 1 and 3 with respect to the simulations are similar in magnitude to those from National Oceanic and Atmospheric Administration-18 AMSU-A. The MWTS biases at channels 2 and 4 are larger than AMSU-A.