This paper demonstrates a polarimetric pressure measurement using a multimode phase retarder plastic optical fiber fabricated from a birefringence-controllable copolymer. An optimal composition that gives the most pronounced response to pressure was studied by comparing the extinction ratio of fibers fabricated with different copolymer compositions. A simple sensor design with a single-fiber structure was proposed that has detection capabilities similar to those of the conventional dual-path structure of a Mach-Zehnder interferometer. A linear relationship between the fiber birefringence and the applied pressure was observed in a range from 0 to 0.06 MPa. A polarimetric sensitivity of 1.56 x 10(-5) MPa(-1) was obtained experimentally from the relationship between the birefringence and pressure.