['The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway plays a role in various biological processes. Phosphorylated STAT3 (p-STAT3) functions as a transcriptional factor, and suppressor of cytokine signaling 3 (SOCS3) is a potential inhibitor of STAT3. Here, we analyzed the status of the JAK-STAT pathway in undifferentiated pleomorphic sarcoma (UPS).', 'We performed immunohistochemistry in 79 samples of UPS and Western blotting in 10 frozen samples. We also examined alterations in protein expression in the JAK-STAT pathway after the inhibition of phosphorylated Akt (p-Akt) or extracellular signal-regulated kinase (p-Erk) in vitro.', 'Immunohistochemically, p-STAT3 and SOCS3 were positive in 59.7 and 55.8%, respectively. Positivity for p-STAT3 was significantly correlated with a better prognosis (p = 0.0006) and negatively with SOCS3 expression (p = 0.0223). Positivity for SOCS3 was significantly correlated with a worse prognosis (p = 0.0001). Western blotting analysis revealed that p-STAT3 expression was lower in tumor than in normal tissue. In vitro results demonstrated that there was no detectable change in the expression of p-STAT3 regardless of the status of p-Akt or p-Erk.'] Does phosphorylation of STAT3 in Undifferentiated Pleomorphic Sarcoma be Correlated with a Favorable Prognosis?