Prostate cancer is one of the most common types of cancer in men in Western countries. Chronic inflammation in the prostate, regulated by a complex network of factors including inflammatory cytokines, is one of the established risk factors for development of prostate cancer. Interleukin-6 (IL-6) is a well-known promoter of inflammation-induced carcinogenesis and disease progression in prostate cancer. Presence in the prostate and possible roles in tumor development by other members of the IL-6 family of cytokines have, however, been less studied. Here we show that the IL-6-type cytokine oncostatin M (OSM) indeed induce cellular properties associated with tumorigenesis and disease progression in non-transformed human prostate epithelial cells, including morphological changes, epithelial-to-mesenchymal transition (EMT), enhanced migration and pro-invasive growth patterns. The effects by OSM were partly mediated by activation of signal transducer and activator of transcription 3 (STAT3), a transcription factor established as driver of cancer progression and treatment resistance in numerous types of cancer. The findings presented here further consolidate IL-6-type cytokines and STAT3 as promising future treatment targets for prostate cancer.