Synopsis:The origin of ridging phenomenon in 18% Cr ferritic stainless steel sheet was studied and the following results were obtained.(1) Macroscopic stripe pattern which was composed of many dark and bright microscopic stripes running along the rolling direction of sheet was observed on the surface of sheet when it was severely etched.(2) Macroscopic and microscopic stripes corresponded with large and small undulations of ridging, respectively, which was appeared after stretching of sheet.(3) Line analysis with EPMA across the dark and bright zones in stripe pattern showed clear segregation of chromium and carbon.(4) This segregation was inherited from the two-phase structuse, austenite and ferrite, in hot rolled sheet and was hold even in cold rolled and annealed sheet. Each segregation zone was extended by cold rolling and made a stripe pattern on the surface of sheet.