Graphene oxide (GO)/graphene (GN) nanosheets were coated onto the poly(glycidyl methacrylate-ethylene dimethacrylate) monolithic bed synthesized inside the capillary in order to prepare a promising polymer monolith microextraction (PMME) material (GO/GN@poly(GMA-EDMA)). Various techniques, including Fourier transform infrared spectroscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy, were employed to characterize the synthesized GO/GN@poly(GMA-EDMA) monoliths, confirming that GO/GN was effectively functionalized on the poly(GMA-EDMA) monolithic materials. Furthermore, a new method was developed for the analysis of sarcosine (identified as a potential prostate cancer biomarker) using PMME coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Under the preoptimized conditions, the monolithic column afforded satisfactory enhancement factor (32-fold) and low limits of detection (1.0 ng mL⁻¹) were obtained. In comparison to several other commercialized solid phase extraction adsorbents, GN@poly(GMA-EDMA) monoliths exhibited excellent performance with recoveries of sarcosine approaching 93% with relative standard deviations less than 11.5%.