Monitoring the concentrations of theophylline in biological samples is crucial due to its narrow therapeutic range and potential toxicity. This study presents the development of a boron-doped diamond (BDD) and titanium dioxide (TiO2)-modified screen-printed carbon electrode (SPCE) for the rapid electrochemical detection of theophylline in urine samples. The SPCE/BDD-TiO2 single-layer (SL) sensor was synthesized using anodization and drop-casting methods, as confirmed by XRD, FTIR, and SEM-EDX characterizations. Electrochemical characterization confirmed the capacitive nature and high surface area of the synthesized electrode. The SPCE/BDD-TiO2 SL sensor exhibited a low limit of detection (LOD) of 5.76 μM within a linear range of 50 to 250 μM, outperforming unmodified SPCE, SPCE/BDD, SPCE/TiO2 and SPCE/BDD/TiO2 double-layer (DL). In addition, the SPCE/BDD-TiO2 SL also demonstrated selective properties toward glucose, uric acid, and urea. Analysis in artificial urine demonstrated a recovery rate of 105.32 %, with excellent repeatability. The electrochemical signals showed an RSD of 0.15 % over 10 times measurements, and good stability was observed over three months. These results suggest that the electrode holds promising potential for the determination of theophylline in clinical applications. © 2025 Elsevier B.V.