An apparatus and method for controlling acoustic echo cancellation in a mobile communication terminal are capable of improving phenomena occurring during a call, such as an echo phenomenon, muting phenomenon and fluctuation of transmitting signals, by performing real-time monitoring of the signal of a speaker output stage and effectively controlling an AEC function according to the characteristics of the terminal. The level of a receiving signal which is outputted to a speaker is detected. A transmitting signal, which is outputted from a microphone, is converted into a digital voice signal. A certain attenuation value is adaptively determined depending on the detected level of the receiving signal, and attenuation on transmitting signal is controlled according to the determined attenuation value.