A method and an apparatus for de-mapping symbols in a Multi-Input Multi-Output (MIMO) system are provided. In the present invention, an estimated channel effect and a plurality of received data symbols are used to estimate a plurality of transmitted data symbols. A plurality of constellation points around an estimated value are selected as the detected values of the transmitted data symbol after the estimated value of one of the transmitted data symbols is calculated. Then, the detected values are used to calculate the detected values of remaining transmitted data symbols separately so as to obtain a plurality of detected value sets. Finally, a best one among the detected value sets is chosen as a result of de-mapping the received symbols. Therefore, only a few detected value sets are calculated and a better detected result is obtained, which possesses low complexity and high performance.