Signal transducers and activators of transcription (STATs) play a pleomorphic role in signal transduction, similarly to an oncogene. Suppressors of cytokine signaling (SOCS) inhibit STAT pathways. In breast cancer, little is known about the correlation among STATs, SOCS, and clinicopathological/biological features. Therefore, we investigated p-STAT3 (activated form of STAT3) and SOCS-1/3 expression, and clarified their correlation. Immunohistochemical staining for p-STAT3 antigen was performed in 74 surgically resected primary breast cancers. Real-time RT-PCR was used to measure mRNA expression of SOCS-1 and SOCS-3. There were no significant correlations between p-STAT3 expression and clinicopathological/biological features. SOCS-3 mRNA expression in the lymph node-positive group was significantly lower than that in the negative group (p=0.013). Among three groups divided based on the number of involved lymph nodes (node-negative group, 1-3 involved nodes group, 4 or more involved nodes group), the group with 4 or more involved nodes had the lowest expression of SOCS-3 (p=0.043). Correlations were not seen between SOCS-1 and SOCS-3 expression and other clinicopathological/biological features, except for blood vessel invasion. There were no statistical correlations between either SOCS-1 or SOCS-3 mRNA expression and p-STAT3 expression. Reduced expression of SOCS-3 is closely related to lymph node metastasis. Therefore, SOCS-3 may be a good predictor for lymph node metastasis.