A novel concurrent core test approach is proposed to reduce the test cost of SOC. Prior to the application of test, the test sets corresponding to cores under test (CUT) are merged by using the proposed merging algorithm to obtain a minimum size of merged test set. During test, the proposed scan tree architecture is employed to support the concurrent core test using the merged test set. The approach achieves concurrent core test with one scan input and low hardware overhead. Moreover, the approach does not need any additional test generation, and it can be used in conjunction with general compression/decompression techniques to further reduce test cost. Experimental results for ISCAS 89 benchmarks have proven the efficiency of the proposed approach.