Introduction:We have studied the prevalence of the rectosigmoid inflammation and its associated risk factors in patient with Ankylosing Spondylitis.Materials and Methods:In this cross-sectional study,110 patients who have the diagnosis of AS were enrolled.Patients who were on biological agents or Sulfasalazine were excluded.Demographic data,disease severity,HLA B27 status,latest CRP and ESR level and also fecal Calprotectin were collected.All patients underwent rectosigmoidoscopy and biopsy.Data analysis was done using SPSS software(18).