Optical fiber technology plays a critical role in modern neuroscience towards understanding the complex neuronal dynamics within the nervous system. In this study, we manufactured and characterized amorphous thermally drawn poly D, L-lactic acid (PDLLA) biodegradable optical fibers in different diameters. These optical fibers were then implanted into the lateral posterior region of the mouse brain for four months, allowing us to assess their degradation characteristics. The gradual dissolution of the implanted PDLLA optical fibers in the brain was confirmed by optical, photoacoustic, and scanning electron microscopy (SEM), light propagation characteristics, and molecular weight measurements. The results indicate that the degradation rate of the biodegradable optical fiber was mainly pronounced during the first week. After four months, degradation led to the formation of micropores on the surface of the implanted fiber within the gray matter region of the brain. We believe that the PDLLA biodegradable optical fiber developed in this study constitutes a promising candidate for further functionalization and development of next-generation biocompatible, soft, and biodegradable bi-directional neural interfaces.