We collected 14 low-grade paired Undifferentiated spindle cell sarcoma (USCS) to conduct a comprehensive mass spectrometry (MS) proteomic analysis on USCSs, while also comparing the clinicopathologic characteristics of low-grade USCSs and UPSs. More than 5600 proteins could be identified. Low-grade USCSs had 353 up-regulated and 500 down-regulated proteins compared to corresponding normal tissue.