Provided is a channel estimation apparatus and method in a broadband wireless communications system using a smart antenna are provided. In the channel estimation apparatus, an FFT processor converts a received time-domain signal into a frequency-domain signal by FFT-processing the received time-domain signal. A channel acquirer estimates a first channel information for an SDMA user using a preamble signal allocated to the SDMA user in the frequency-domain signal. A channel tracker estimates a second channel information for the SDMA user using pilots in a data area allocated to the SDMA user in the frequency-domain signal. A channel estimator estimates a final channel information by weighting the first channel information and the second channel information according to a channel change rate.