Cancer-testis (CT) antigens have promise as targets for immunotherapy, because of their restricted expression in tumor or testis tissue. MAGEA4 is both a MAGE family member and a CT antigen, and has attracted attention as a potential immunotherapeutic target. We investigated MAGEA4 expression by immunohistochemistry in bone and soft tissue tumor specimens that consisted of 35 malignant or intermediate and 24 benign histological subtypes, in order to evaluate its possible utility as an immunotherapy target and its potential use as a diagnostic marker when combined with another CT antigen, NY-ESO-1. Among these tumors, MAGEA4 was detected in 82.2% of synovial sarcomas, 67.7% of myxoid liposarcomas, 43.8% of osteosarcomas, 41.4% of angiosarcomas, 24.6% of malignant peripheral nerve sheath tumors (MPNSTs), and 21.4% of chondrosarcomas. NY-ESO-1 expression was found in 88.2% of myxoid liposarcomas, 61.1% of synovial sarcomas, 31.3% of osteosarcomas, 21.4% of pleomorphic liposarcomas, 16.7% of desmoplastic small round cell tumors, and 14.3% of chondrosarcomas. Benign tumors and non-tumorous tissue, except for testis tissue, did not express MAGEA4 or NY-ESO-1. Combined use of MAGEA4 and NY-ESO-1 increased the sensitivity, specificity, positive predictive values, and negative predictive values for distinguishing synovial sarcoma from spindle cell tumors and other mimicking tumors, compared to individual use of MAGEA4 or NY-ESO-1. Our results support the immunotherapy targeting MAGEA4 or NY-ESO-1 can be an ancillary therapy in the above-mentioned tumors, and the potential utility of MAGEA4 as an ancillary diagnostic marker for synovial sarcoma combined with NY-ESO-1.