The family of signal transducers and activators of transcription (STAT) are transcription factors. Among them, STAT1 is associated with an apoptosis pathway, while STAT3 is associated with tumorigenicity in various cancer cells. In order to investigate the primary roles of STAT1 and STAT3 in head and neck squamous cell carcinoma (HNSCC), we blocked STAT3 with two JAK inhibitors: AG490 (JAK2-STAT3 pathway inhibitor) and JAK total inhibitor. When we inhibited STAT3 with AG490, significant cell death was observed. However, in the case of JAK kinase total inhibitor, no cell growth retardation was observed. We focused on the role of STAT1 in this phenomenon. Suppression of STAT1 by si-RNA resulted in increased cell survival. Furthermore, the growth inhibitory effect of AG490 was reduced by treatment with si-RNA of STAT1. These results reveal that STAT1 is required to promote the tumor killing effect of STAT3 inhibition in HNSCC.