A concentric cylinder apparatus for the studies of flow dichroism in polymer solutions is described in detail. The outer and inner cylinders are both made of fused quartz which is transparent in visible and ultraviolet region down to 220 mμ. The velocity gradient is produced in solution in the gap between the cylinders by rotating the inner one. The light path is designed to be perpendicular to the axis of rotation of the quartz cylinder. A differential device makes it possible to measure the difference in absorption coefficients, ε‖ and ε⊥, which are the absorption coefficients measured by plane-polarized light having parallel and perpendicular electric vector with the stream line. The apparatus is found to be useful for studying the regularity of orientation of chromophores in both synthetic and biological polymer chains.