We present a microstructured polymer fiber dedicated to long period grating (LPGs) inscription using a focused UV laser beam. The core and the microstructured cladding of the developed fiber are made of pure poly(methyl methacrylate) (PMMA). The external layer of the solid part of the cladding has increased UV absorption due to doping with trans-4-stilbenemethanol, which shows an absorption band at around 310 nm related to trans-cis photoisomerization. We present transmission characteristics of LPGs fabricated in this fiber using the point-by-point inscription technique with a He-Cd laser beam of 325 nm wavelength. We also demonstrate that in the proposed fiber, the fabrication process is shortened six times compared to pure PMMA fibers. Moreover, we report on temperature response and long-term stability of the fabricated gratings.