The present invention relates to 5-thia-omega-substituted phenylprostaglandin E derivatives of the formula (I)(wherein, all the symbols are as defined in the specification), process for producing them and pharmaceutical compositions comprising them as active ingredient.The compounds of the formula (I) can bind to PGE2 receptors (especially, subtype EP4) strongly, so they are expected to be useful for prevention and/or treatment of immunological diseases (autoimmune diseases such as amyotrophic lateral sclerosis (ALS), multiple sclerosis, Sjoegren's syndrome, chronic rheumarthrosis and systemic lupus erythematosus etc., and rejection after organ transplantation etc.), asthma, abnormal bone formation, neuronal cell death, lung failure, liver damage, acute hepatitis, nephritis, renal insufficiency, hypertension, myocardiac ischemia, systemic inflammatory response syndrome, ambustion pain, sepsis, hemophagous syndrome, macrophage activation syndrome, Still's disease, Kawasaki disease, burn, systemic granulomatosis, ulcerative colitis, Crohn's disease, hypercytokinemia at dialysis, multiple organ failure, and shock etc. Further, it is thought that EP4 subtype receptor relates to sleeping disorder and blood platelet aggregation, so the compounds of the present invention are expected to be useful for the prevention and/or treatment of such diseases.