We have investigated the anisotropic decomposition of polyimide (poly[bis(4,4'-oxydiphenylene)-dimetylmetyl-pyromellitimide]) molecules induced by exposure to linearly polarized ultraviolet light (LPUVL) of wavelength similar to 300 nm. The decomposition of the polyimide molecule was monitored by measuring the polarized infrared (IR) absorption spectra as a function of LPUVL exposure. We propose an empirical equation that describes the relation between the orientational distribution of polyimide chains and LPUVL exposure. We consider two decomposition rates beta (//) and beta (perpendicular to) for the polyimide chains oriented parallel and perpendicular to the polarization direction of LPUVL, respectively. By taking account of the increase the decomposition rates around 30 J(.)cm(-2), the IR absorption data could be reproduced with beta (//)/beta (perpendicular to) = 1.23 +/- 0.02. The decomposition rate beta (//) is (4.5 +/-1.0) x 10(-3)J(-1.)cm(2) for the LPUVL exposure range up to similar to 30 J cm, and (1.6 +/- 0.1) x 10(-2) J(-1.)cm(2) beyond similar to 30 J.cm(-2).