Provided are an apparatus and method for selecting an optimal signal using auxiliary equalization in a diversity receiver. The optimal signal selecting apparatus includes: a plurality of sync recovery units for extracting sync information from baseband signals, which are candidate signals, except a baseband signal selected as a current optimal signal a plurality of auxiliary equalizers for channel-equalizing the candidate signals based on the extracted sync information; a plurality of SNR measuring units for measuring signal-to-noise ratios (SNRs) of the candidate signals inputted to the auxiliary equalizers and the candidates signals equalized in the auxiliary equalizers; and an optimal signal selector for selecting an optimal candidate signal from the candidate signals by using the extracted sync information and the measured SNRs, and replacing the optimal signal with the optimal candidate signal when reception quality of the current optimal signal is poor.